Refactor toJson/fillJson

Both now use through a common JsonConverter<> template class with its
base definition tuned for structs/QJsonObjects and specialisations for
non-object types. This new implementation doesn't work with virtual
fillJson functions yet (so EventContent classes still use toJson as a
member function) and does not cope quite well with non-constructible
objects (you have to specialise JsonConverter<> rather than, more
intuitively, JsonObjectConverter<>), but overall is more streamlined
compared to the previous implementation. It also fixes one important
issue that pushed for a rewrite: the previous implementation was not
working with structure hierarchies at all so (in particular) the Filter
part of CS API was totally disfunctional.

80 files changed, 851 insertions, 1100 deletions

diff --git a/lib/application-service/definitions/location.cpp b/lib/application-service/definitions/location.cpp
index 958a55bf..a53db8d7 100644
--- a/lib/application-service/definitions/location.cpp
+++ b/lib/application-service/definitions/location.cpp
@@ -6,25 +6,19 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const ThirdPartyLocation& pod)
+void JsonObjectConverter<ThirdPartyLocation>::dumpTo(
+        QJsonObject& jo, const ThirdPartyLocation& pod)
 {
-    QJsonObject jo;
     addParam<>(jo, QStringLiteral("alias"), pod.alias);
     addParam<>(jo, QStringLiteral("protocol"), pod.protocol);
     addParam<>(jo, QStringLiteral("fields"), pod.fields);
-    return jo;
 }
 
-ThirdPartyLocation FromJsonObject<ThirdPartyLocation>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<ThirdPartyLocation>::fillFrom(
+    const QJsonObject& jo, ThirdPartyLocation& result)
 {
-    ThirdPartyLocation result;
-    result.alias =
-        fromJson<QString>(jo.value("alias"_ls));
-    result.protocol =
-        fromJson<QString>(jo.value("protocol"_ls));
-    result.fields =
-        fromJson<QJsonObject>(jo.value("fields"_ls));
-
-    return result;
+    fromJson(jo.value("alias"_ls), result.alias);
+    fromJson(jo.value("protocol"_ls), result.protocol);
+    fromJson(jo.value("fields"_ls), result.fields);
 }
 
diff --git a/lib/application-service/definitions/location.h b/lib/application-service/definitions/location.h
index 89b48a43..5586cfc6 100644
--- a/lib/application-service/definitions/location.h
+++ b/lib/application-service/definitions/location.h
@@ -21,12 +21,10 @@ namespace QMatrixClient
         /// Information used to identify this third party location.
         QJsonObject fields;
     };
-
-    QJsonObject toJson(const ThirdPartyLocation& pod);
-
-    template <> struct FromJsonObject<ThirdPartyLocation>
+    template <> struct JsonObjectConverter<ThirdPartyLocation>
     {
-        ThirdPartyLocation operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const ThirdPartyLocation& pod);
+        static void fillFrom(const QJsonObject& jo, ThirdPartyLocation& pod);
     };
 
 } // namespace QMatrixClient
diff --git a/lib/application-service/definitions/protocol.cpp b/lib/application-service/definitions/protocol.cpp
index 04bb7dfc..2a62b15d 100644
--- a/lib/application-service/definitions/protocol.cpp
+++ b/lib/application-service/definitions/protocol.cpp
@@ -6,75 +6,55 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const FieldType& pod)
+void JsonObjectConverter<FieldType>::dumpTo(
+        QJsonObject& jo, const FieldType& pod)
 {
-    QJsonObject jo;
     addParam<>(jo, QStringLiteral("regexp"), pod.regexp);
     addParam<>(jo, QStringLiteral("placeholder"), pod.placeholder);
-    return jo;
 }
 
-FieldType FromJsonObject<FieldType>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<FieldType>::fillFrom(
+    const QJsonObject& jo, FieldType& result)
 {
-    FieldType result;
-    result.regexp =
-        fromJson<QString>(jo.value("regexp"_ls));
-    result.placeholder =
-        fromJson<QString>(jo.value("placeholder"_ls));
-
-    return result;
+    fromJson(jo.value("regexp"_ls), result.regexp);
+    fromJson(jo.value("placeholder"_ls), result.placeholder);
 }
 
-QJsonObject QMatrixClient::toJson(const ProtocolInstance& pod)
+void JsonObjectConverter<ProtocolInstance>::dumpTo(
+        QJsonObject& jo, const ProtocolInstance& pod)
 {
-    QJsonObject jo;
     addParam<>(jo, QStringLiteral("desc"), pod.desc);
     addParam<IfNotEmpty>(jo, QStringLiteral("icon"), pod.icon);
     addParam<>(jo, QStringLiteral("fields"), pod.fields);
     addParam<>(jo, QStringLiteral("network_id"), pod.networkId);
-    return jo;
 }
 
-ProtocolInstance FromJsonObject<ProtocolInstance>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<ProtocolInstance>::fillFrom(
+    const QJsonObject& jo, ProtocolInstance& result)
 {
-    ProtocolInstance result;
-    result.desc =
-        fromJson<QString>(jo.value("desc"_ls));
-    result.icon =
-        fromJson<QString>(jo.value("icon"_ls));
-    result.fields =
-        fromJson<QJsonObject>(jo.value("fields"_ls));
-    result.networkId =
-        fromJson<QString>(jo.value("network_id"_ls));
-
-    return result;
+    fromJson(jo.value("desc"_ls), result.desc);
+    fromJson(jo.value("icon"_ls), result.icon);
+    fromJson(jo.value("fields"_ls), result.fields);
+    fromJson(jo.value("network_id"_ls), result.networkId);
 }
 
-QJsonObject QMatrixClient::toJson(const ThirdPartyProtocol& pod)
+void JsonObjectConverter<ThirdPartyProtocol>::dumpTo(
+        QJsonObject& jo, const ThirdPartyProtocol& pod)
 {
-    QJsonObject jo;
     addParam<>(jo, QStringLiteral("user_fields"), pod.userFields);
     addParam<>(jo, QStringLiteral("location_fields"), pod.locationFields);
     addParam<>(jo, QStringLiteral("icon"), pod.icon);
     addParam<>(jo, QStringLiteral("field_types"), pod.fieldTypes);
     addParam<>(jo, QStringLiteral("instances"), pod.instances);
-    return jo;
 }
 
-ThirdPartyProtocol FromJsonObject<ThirdPartyProtocol>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<ThirdPartyProtocol>::fillFrom(
+    const QJsonObject& jo, ThirdPartyProtocol& result)
 {
-    ThirdPartyProtocol result;
-    result.userFields =
-        fromJson<QStringList>(jo.value("user_fields"_ls));
-    result.locationFields =
-        fromJson<QStringList>(jo.value("location_fields"_ls));
-    result.icon =
-        fromJson<QString>(jo.value("icon"_ls));
-    result.fieldTypes =
-        fromJson<QHash<QString, FieldType>>(jo.value("field_types"_ls));
-    result.instances =
-        fromJson<QVector<ProtocolInstance>>(jo.value("instances"_ls));
-
-    return result;
+    fromJson(jo.value("user_fields"_ls), result.userFields);
+    fromJson(jo.value("location_fields"_ls), result.locationFields);
+    fromJson(jo.value("icon"_ls), result.icon);
+    fromJson(jo.value("field_types"_ls), result.fieldTypes);
+    fromJson(jo.value("instances"_ls), result.instances);
 }
 
diff --git a/lib/application-service/definitions/protocol.h b/lib/application-service/definitions/protocol.h
index 2aca7d66..0a1f9a21 100644
--- a/lib/application-service/definitions/protocol.h
+++ b/lib/application-service/definitions/protocol.h
@@ -25,12 +25,10 @@ namespace QMatrixClient
         /// An placeholder serving as a valid example of the field value.
         QString placeholder;
     };
-
-    QJsonObject toJson(const FieldType& pod);
-
-    template <> struct FromJsonObject<FieldType>
+    template <> struct JsonObjectConverter<FieldType>
     {
-        FieldType operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const FieldType& pod);
+        static void fillFrom(const QJsonObject& jo, FieldType& pod);
     };
 
     struct ProtocolInstance
@@ -45,12 +43,10 @@ namespace QMatrixClient
         /// A unique identifier across all instances.
         QString networkId;
     };
-
-    QJsonObject toJson(const ProtocolInstance& pod);
-
-    template <> struct FromJsonObject<ProtocolInstance>
+    template <> struct JsonObjectConverter<ProtocolInstance>
     {
-        ProtocolInstance operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const ProtocolInstance& pod);
+        static void fillFrom(const QJsonObject& jo, ProtocolInstance& pod);
     };
 
     struct ThirdPartyProtocol
@@ -78,12 +74,10 @@ namespace QMatrixClient
         /// same application service.
         QVector<ProtocolInstance> instances;
     };
-
-    QJsonObject toJson(const ThirdPartyProtocol& pod);
-
-    template <> struct FromJsonObject<ThirdPartyProtocol>
+    template <> struct JsonObjectConverter<ThirdPartyProtocol>
     {
-        ThirdPartyProtocol operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const ThirdPartyProtocol& pod);
+        static void fillFrom(const QJsonObject& jo, ThirdPartyProtocol& pod);
     };
 
 } // namespace QMatrixClient
diff --git a/lib/application-service/definitions/user.cpp b/lib/application-service/definitions/user.cpp
index ca334236..8ba92321 100644
--- a/lib/application-service/definitions/user.cpp
+++ b/lib/application-service/definitions/user.cpp
@@ -6,25 +6,19 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const ThirdPartyUser& pod)
+void JsonObjectConverter<ThirdPartyUser>::dumpTo(
+        QJsonObject& jo, const ThirdPartyUser& pod)
 {
-    QJsonObject jo;
     addParam<>(jo, QStringLiteral("userid"), pod.userid);
     addParam<>(jo, QStringLiteral("protocol"), pod.protocol);
     addParam<>(jo, QStringLiteral("fields"), pod.fields);
-    return jo;
 }
 
-ThirdPartyUser FromJsonObject<ThirdPartyUser>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<ThirdPartyUser>::fillFrom(
+    const QJsonObject& jo, ThirdPartyUser& result)
 {
-    ThirdPartyUser result;
-    result.userid =
-        fromJson<QString>(jo.value("userid"_ls));
-    result.protocol =
-        fromJson<QString>(jo.value("protocol"_ls));
-    result.fields =
-        fromJson<QJsonObject>(jo.value("fields"_ls));
-
-    return result;
+    fromJson(jo.value("userid"_ls), result.userid);
+    fromJson(jo.value("protocol"_ls), result.protocol);
+    fromJson(jo.value("fields"_ls), result.fields);
 }
 
diff --git a/lib/application-service/definitions/user.h b/lib/application-service/definitions/user.h
index 79ca7789..062d2cac 100644
--- a/lib/application-service/definitions/user.h
+++ b/lib/application-service/definitions/user.h
@@ -21,12 +21,10 @@ namespace QMatrixClient
         /// Information used to identify this third party location.
         QJsonObject fields;
     };
-
-    QJsonObject toJson(const ThirdPartyUser& pod);
-
-    template <> struct FromJsonObject<ThirdPartyUser>
+    template <> struct JsonObjectConverter<ThirdPartyUser>
     {
-        ThirdPartyUser operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const ThirdPartyUser& pod);
+        static void fillFrom(const QJsonObject& jo, ThirdPartyUser& pod);
     };
 
 } // namespace QMatrixClient
diff --git a/lib/converters.cpp b/lib/converters.cpp
index 41a9a65e..88f5267e 100644
--- a/lib/converters.cpp
+++ b/lib/converters.cpp
@@ -22,38 +22,34 @@
 
 using namespace QMatrixClient;
 
-QJsonValue QMatrixClient::variantToJson(const QVariant& v)
+QJsonValue JsonConverter<QVariant>::dump(const QVariant& v)
 {
     return QJsonValue::fromVariant(v);
 }
 
-QJsonObject QMatrixClient::toJson(const QVariantMap& map)
+QVariant JsonConverter<QVariant>::load(const QJsonValue& jv)
 {
-    return QJsonObject::fromVariantMap(map);
+    return jv.toVariant();
 }
 
-#if (QT_VERSION >= QT_VERSION_CHECK(5, 5, 0))
-QJsonObject QMatrixClient::toJson(const QVariantHash& hMap)
+QJsonObject JsonConverter<variant_map_t>::dump(const variant_map_t& map)
 {
-    return QJsonObject::fromVariantHash(hMap);
-}
+    return
+#if (QT_VERSION >= QT_VERSION_CHECK(5, 5, 0))
+        QJsonObject::fromVariantHash
+#else
+        QJsonObject::fromVariantMap
 #endif
-
-QVariant FromJson<QVariant>::operator()(const QJsonValue& jv) const
-{
-    return jv.toVariant();
+        (map);
 }
 
-QMap<QString, QVariant>
-FromJson<QMap<QString, QVariant>>::operator()(const QJsonValue& jv) const
+variant_map_t JsonConverter<QVariantHash>::load(const QJsonValue& jv)
 {
-    return jv.toObject().toVariantMap();
-}
-
+    return jv.toObject().
 #if (QT_VERSION >= QT_VERSION_CHECK(5, 5, 0))
-QHash<QString, QVariant>
-FromJson<QHash<QString, QVariant>>::operator()(const QJsonValue& jv) const
-{
-    return jv.toObject().toVariantHash();
-}
+        toVariantHash
+#else
+        toVariantMap
 #endif
+        ();
+}
diff --git a/lib/converters.h b/lib/converters.h
index 53855a1f..6227902d 100644
--- a/lib/converters.h
+++ b/lib/converters.h
@@ -57,238 +57,221 @@ class QVariant;
 
 namespace QMatrixClient
 {
-    // This catches anything implicitly convertible to QJsonValue/Object/Array
-    inline auto toJson(const QJsonValue& val) { return val; }
-    inline auto toJson(const QJsonObject& o) { return o; }
-    inline auto toJson(const QJsonArray& arr) { return arr; }
-    // Special-case QString to avoid ambiguity between QJsonValue
-    // and QVariant (also, QString.isEmpty() is used in _impl::AddNode<> below)
-    inline auto toJson(const QString& s) { return s; }
-
-    inline QJsonArray toJson(const QStringList& strings)
-    {
-        return QJsonArray::fromStringList(strings);
-    }
-
-    inline QString toJson(const QByteArray& bytes)
+    template <typename T>
+    struct JsonObjectConverter
     {
-        return bytes.constData();
-    }
+        static void dumpTo(QJsonObject& jo, const T& pod) { jo = pod; }
+        static void fillFrom(const QJsonObject& jo, T& pod) { pod = jo; }
+    };
 
-    // QVariant is outrageously omnivorous - it consumes whatever is not
-    // exactly matching the signature of other toJson overloads. The trick
-    // below disables implicit conversion to QVariant through its numerous
-    // non-explicit constructors.
-    QJsonValue variantToJson(const QVariant& v);
     template <typename T>
-    inline auto toJson(T&& /* const QVariant& or QVariant&& */ var)
-        -> std::enable_if_t<std::is_same<std::decay_t<T>, QVariant>::value,
-                            QJsonValue>
+    struct JsonConverter
     {
-        return variantToJson(var);
-    }
-    QJsonObject toJson(const QMap<QString, QVariant>& map);
-#if (QT_VERSION >= QT_VERSION_CHECK(5, 5, 0))
-    QJsonObject toJson(const QHash<QString, QVariant>& hMap);
-#endif
+        static QJsonObject dump(const T& pod)
+        {
+            QJsonObject jo;
+            JsonObjectConverter<T>::dumpTo(jo, pod);
+            return jo;
+        }
+        static T doLoad(const QJsonObject& jo)
+        {
+            T pod;
+            JsonObjectConverter<T>::fillFrom(jo, pod);
+            return pod;
+        }
+        static T load(const QJsonValue& jv) { return doLoad(jv.toObject()); }
+        static T load(const QJsonDocument& jd) { return doLoad(jd.object()); }
+    };
 
     template <typename T>
-    inline QJsonArray toJson(const std::vector<T>& vals)
+    inline auto toJson(const T& pod)
     {
-        QJsonArray ar;
-        for (const auto& v: vals)
-            ar.push_back(toJson(v));
-        return ar;
+        return JsonConverter<T>::dump(pod);
     }
 
     template <typename T>
-    inline QJsonArray toJson(const QVector<T>& vals)
+    inline auto fillJson(QJsonObject& json, const T& data)
     {
-        QJsonArray ar;
-        for (const auto& v: vals)
-            ar.push_back(toJson(v));
-        return ar;
+        JsonObjectConverter<T>::dumpTo(json, data);
     }
 
     template <typename T>
-    inline QJsonObject toJson(const QSet<T>& set)
+    inline auto fromJson(const QJsonValue& jv)
     {
-        QJsonObject json;
-        for (auto e: set)
-            json.insert(toJson(e), QJsonObject{});
-        return json;
+        return JsonConverter<T>::load(jv);
     }
 
     template <typename T>
-    inline QJsonObject toJson(const QHash<QString, T>& hashMap)
+    inline T fromJson(const QJsonDocument& jd)
     {
-        QJsonObject json;
-        for (auto it = hashMap.begin(); it != hashMap.end(); ++it)
-            json.insert(it.key(), toJson(it.value()));
-        return json;
+        return JsonConverter<T>::load(jd);
     }
 
     template <typename T>
-    inline QJsonObject toJson(const std::unordered_map<QString, T>& hashMap)
+    inline void fromJson(const QJsonValue& jv, T& pod)
     {
-        QJsonObject json;
-        for (auto it = hashMap.begin(); it != hashMap.end(); ++it)
-            json.insert(it.key(), toJson(it.value()));
-        return json;
+        pod = fromJson<T>(jv);
     }
 
     template <typename T>
-    struct FromJsonObject
+    inline void fromJson(const QJsonDocument& jd, T& pod)
     {
-        T operator()(const QJsonObject& jo) const { return T(jo); }
-    };
+        pod = fromJson<T>(jd);
+    }
 
+    // Unfolds Omittable<>
     template <typename T>
-    struct FromJson
+    inline void fromJson(const QJsonValue& jv, Omittable<T>& pod)
     {
-        T operator()(const QJsonValue& jv) const
-        {
-            return FromJsonObject<T>()(jv.toObject());
-        }
-        T operator()(const QJsonDocument& jd) const
-        {
-            return FromJsonObject<T>()(jd.object());
-        }
-    };
+        pod = fromJson<T>(jv);
+    }
 
     template <typename T>
-    inline auto fromJson(const QJsonValue& jv)
+    inline void fillFromJson(const QJsonValue& jv, T& pod)
     {
-        return FromJson<T>()(jv);
+        JsonObjectConverter<T>::fillFrom(jv.toObject(), pod);
     }
 
+    // JsonConverter<> specialisations
+
     template <typename T>
-    inline auto fromJson(const QJsonDocument& jd)
+    struct TrivialJsonDumper
     {
-        return FromJson<T>()(jd);
-    }
+        // Works for: QJsonValue (and all things it can consume),
+        // QJsonObject, QJsonArray
+        static auto dump(const T& val) { return val; }
+    };
 
-    template <> struct FromJson<bool>
+    template <> struct JsonConverter<bool> : public TrivialJsonDumper<bool>
     {
-        auto operator()(const QJsonValue& jv) const { return jv.toBool(); }
+        static auto load(const QJsonValue& jv) { return jv.toBool(); }
     };
 
-    template <> struct FromJson<int>
+    template <> struct JsonConverter<int> : public TrivialJsonDumper<int>
     {
-        auto operator()(const QJsonValue& jv) const { return jv.toInt(); }
+        static auto load(const QJsonValue& jv) { return jv.toInt(); }
     };
 
-    template <> struct FromJson<double>
+    template <> struct JsonConverter<double>
+        : public TrivialJsonDumper<double>
     {
-        auto operator()(const QJsonValue& jv) const { return jv.toDouble(); }
+        static auto load(const QJsonValue& jv) { return jv.toDouble(); }
     };
 
-    template <> struct FromJson<float>
+    template <> struct JsonConverter<float> : public TrivialJsonDumper<float>
     {
-        auto operator()(const QJsonValue& jv) const { return float(jv.toDouble()); }
+        static auto load(const QJsonValue& jv) { return float(jv.toDouble()); }
     };
 
-    template <> struct FromJson<qint64>
+    template <> struct JsonConverter<qint64>
+        : public TrivialJsonDumper<qint64>
     {
-        auto operator()(const QJsonValue& jv) const { return qint64(jv.toDouble()); }
+        static auto load(const QJsonValue& jv) { return qint64(jv.toDouble()); }
     };
 
-    template <> struct FromJson<QString>
+    template <> struct JsonConverter<QString>
+        : public TrivialJsonDumper<QString>
     {
-        auto operator()(const QJsonValue& jv) const { return jv.toString(); }
+        static auto load(const QJsonValue& jv) { return jv.toString(); }
     };
 
-    template <> struct FromJson<QDateTime>
+    template <> struct JsonConverter<QDateTime>
     {
-        auto operator()(const QJsonValue& jv) const
+        static auto dump(const QDateTime& val) = delete; // not provided yet
+        static auto load(const QJsonValue& jv)
         {
-            return QDateTime::fromMSecsSinceEpoch(fromJson<qint64>(jv), Qt::UTC);
+            return QDateTime::fromMSecsSinceEpoch(
+                    fromJson<qint64>(jv), Qt::UTC);
         }
     };
 
-    template <> struct FromJson<QDate>
+    template <> struct JsonConverter<QDate>
     {
-        auto operator()(const QJsonValue& jv) const
+        static auto dump(const QDate& val) = delete; // not provided yet
+        static auto load(const QJsonValue& jv)
         {
             return fromJson<QDateTime>(jv).date();
         }
     };
 
-    template <> struct FromJson<QJsonArray>
+    template <> struct JsonConverter<QJsonArray>
+        : public TrivialJsonDumper<QJsonArray>
     {
-        auto operator()(const QJsonValue& jv) const
-        {
-            return jv.toArray();
-        }
+        static auto load(const QJsonValue& jv) { return jv.toArray(); }
     };
 
-    template <> struct FromJson<QByteArray>
+    template <> struct JsonConverter<QByteArray>
     {
-        auto operator()(const QJsonValue& jv) const
+        static QString dump(const QByteArray& ba) { return ba.constData(); }
+        static auto load(const QJsonValue& jv)
         {
             return fromJson<QString>(jv).toLatin1();
         }
     };
 
-    template <> struct FromJson<QVariant>
+    template <> struct JsonConverter<QVariant>
     {
-        QVariant operator()(const QJsonValue& jv) const;
+        static QJsonValue dump(const QVariant& v);
+        static QVariant load(const QJsonValue& jv);
     };
 
-    template <typename VectorT>
-    struct ArrayFromJson
+    template <typename VectorT,
+              typename T = typename VectorT::value_type>
+    struct JsonArrayConverter
     {
-        auto operator()(const QJsonArray& ja) const
+        static void dumpTo(QJsonArray& ar, const VectorT& vals)
         {
-            using size_type = typename VectorT::size_type;
-            VectorT vect; vect.resize(size_type(ja.size()));
-            std::transform(ja.begin(), ja.end(),
-                           vect.begin(), FromJson<typename VectorT::value_type>());
-            return vect;
+            for (const auto& v: vals)
+                ar.push_back(toJson(v));
         }
-        auto operator()(const QJsonValue& jv) const
+        static auto dump(const VectorT& vals)
         {
-            return operator()(jv.toArray());
+            QJsonArray ja;
+            dumpTo(ja, vals);
+            return ja;
         }
-        auto operator()(const QJsonDocument& jd) const
+        static auto load(const QJsonArray& ja)
         {
-            return operator()(jd.array());
+            VectorT vect; vect.reserve(typename VectorT::size_type(ja.size()));
+            for (const auto& i: ja)
+                vect.push_back(fromJson<T>(i));
+            return vect;
         }
+        static auto load(const QJsonValue& jv) { return load(jv.toArray()); }
+        static auto load(const QJsonDocument& jd) { return load(jd.array()); }
     };
 
-    template <typename T>
-    struct FromJson<std::vector<T>> : ArrayFromJson<std::vector<T>>
+    template <typename T> struct JsonConverter<std::vector<T>>
+        : public JsonArrayConverter<std::vector<T>>
     { };
 
-    template <typename T>
-    struct FromJson<QVector<T>> : ArrayFromJson<QVector<T>>
+    template <typename T> struct JsonConverter<QVector<T>>
+        : public JsonArrayConverter<QVector<T>>
+    { };
+
+    template <typename T> struct JsonConverter<QList<T>>
+        : public JsonArrayConverter<QList<T>>
     { };
 
-    template <typename T> struct FromJson<QList<T>>
+    template <> struct JsonConverter<QStringList>
+        : public JsonConverter<QList<QString>>
     {
-        auto operator()(const QJsonValue& jv) const
+        static auto dump(const QStringList& sl)
         {
-            const auto jsonArray = jv.toArray();
-            QList<T> sl; sl.reserve(jsonArray.size());
-            std::transform(jsonArray.begin(), jsonArray.end(),
-                           std::back_inserter(sl), FromJson<T>());
-            return sl;
+            return QJsonArray::fromStringList(sl);
         }
     };
 
-    template <> struct FromJson<QStringList> : FromJson<QList<QString>> { };
-
-    template <> struct FromJson<QMap<QString, QVariant>>
+    template <> struct JsonObjectConverter<QSet<QString>>
     {
-        QMap<QString, QVariant> operator()(const QJsonValue& jv) const;
-    };
-
-    template <typename T> struct FromJson<QSet<T>>
-    {
-        auto operator()(const QJsonValue& jv) const
+        static void dumpTo(QJsonObject& json, const QSet<QString>& s)
+        {
+            for (const auto& e: s)
+                json.insert(toJson(e), QJsonObject{});
+        }
+        static auto fillFrom(const QJsonObject& json, QSet<QString>& s)
         {
-            const auto json = jv.toObject();
-            QSet<T> s; s.reserve(json.size());
+            s.reserve(s.size() + json.size());
             for (auto it = json.begin(); it != json.end(); ++it)
                 s.insert(it.key());
             return s;
@@ -298,39 +281,44 @@ namespace QMatrixClient
     template <typename HashMapT>
     struct HashMapFromJson
     {
-        auto operator()(const QJsonObject& jo) const
+        static void dumpTo(QJsonObject& json, const HashMapT& hashMap)
+        {
+            for (auto it = hashMap.begin(); it != hashMap.end(); ++it)
+                json.insert(it.key(), toJson(it.value()));
+        }
+        static void fillFrom(const QJsonObject& jo, HashMapT& h)
         {
-            HashMapT h; h.reserve(jo.size());
+            h.reserve(jo.size());
             for (auto it = jo.begin(); it != jo.end(); ++it)
                 h[it.key()] =
                     fromJson<typename HashMapT::mapped_type>(it.value());
-            return h;
-        }
-        auto operator()(const QJsonValue& jv) const
-        {
-            return operator()(jv.toObject());
-        }
-        auto operator()(const QJsonDocument& jd) const
-        {
-            return operator()(jd.object());
         }
     };
 
     template <typename T>
-    struct FromJson<std::unordered_map<QString, T>>
-        : HashMapFromJson<std::unordered_map<QString, T>>
+    struct JsonObjectConverter<std::unordered_map<QString, T>>
+        : public HashMapFromJson<std::unordered_map<QString, T>>
     { };
 
     template <typename T>
-    struct FromJson<QHash<QString, T>> : HashMapFromJson<QHash<QString, T>>
+    struct JsonObjectConverter<QHash<QString, T>>
+        : public HashMapFromJson<QHash<QString, T>>
     { };
 
+    // We could use std::conditional<> below but QT_VERSION* macros in C++ code
+    // cause (kinda valid but useless and noisy) compiler warnings about
+    // bitwise operations on signed integers; so use the preprocessor for now.
+    using variant_map_t =
 #if (QT_VERSION >= QT_VERSION_CHECK(5, 5, 0))
-    template <> struct FromJson<QHash<QString, QVariant>>
+            QVariantHash;
+#else
+            QVariantMap;
+#endif
+    template <> struct JsonConverter<variant_map_t>
     {
-        QHash<QString, QVariant> operator()(const QJsonValue& jv) const;
+        static QJsonObject dump(const variant_map_t& vh);
+        static QVariantHash load(const QJsonValue& jv);
     };
-#endif
 
     // Conditional insertion into a QJsonObject
 
diff --git a/lib/csapi/admin.cpp b/lib/csapi/admin.cpp
index 6066d4d9..ce06a56d 100644
--- a/lib/csapi/admin.cpp
+++ b/lib/csapi/admin.cpp
@@ -16,43 +16,29 @@ namespace QMatrixClient
 {
     // Converters
 
-    template <> struct FromJsonObject<GetWhoIsJob::ConnectionInfo>
+    template <> struct JsonObjectConverter<GetWhoIsJob::ConnectionInfo>
     {
-        GetWhoIsJob::ConnectionInfo operator()(const QJsonObject& jo) const
+        static void fillFrom(const QJsonObject& jo, GetWhoIsJob::ConnectionInfo& result)
         {
-            GetWhoIsJob::ConnectionInfo result;
-            result.ip =
-                fromJson<QString>(jo.value("ip"_ls));
-            result.lastSeen =
-                fromJson<qint64>(jo.value("last_seen"_ls));
-            result.userAgent =
-                fromJson<QString>(jo.value("user_agent"_ls));
-
-            return result;
+            fromJson(jo.value("ip"_ls), result.ip);
+            fromJson(jo.value("last_seen"_ls), result.lastSeen);
+            fromJson(jo.value("user_agent"_ls), result.userAgent);
         }
     };
 
-    template <> struct FromJsonObject<GetWhoIsJob::SessionInfo>
+    template <> struct JsonObjectConverter<GetWhoIsJob::SessionInfo>
     {
-        GetWhoIsJob::SessionInfo operator()(const QJsonObject& jo) const
+        static void fillFrom(const QJsonObject& jo, GetWhoIsJob::SessionInfo& result)
         {
-            GetWhoIsJob::SessionInfo result;
-            result.connections =
-                fromJson<QVector<GetWhoIsJob::ConnectionInfo>>(jo.value("connections"_ls));
-
-            return result;
+            fromJson(jo.value("connections"_ls), result.connections);
         }
     };
 
-    template <> struct FromJsonObject<GetWhoIsJob::DeviceInfo>
+    template <> struct JsonObjectConverter<GetWhoIsJob::DeviceInfo>
     {
-        GetWhoIsJob::DeviceInfo operator()(const QJsonObject& jo) const
+        static void fillFrom(const QJsonObject& jo, GetWhoIsJob::DeviceInfo& result)
         {
-            GetWhoIsJob::DeviceInfo result;
-            result.sessions =
-                fromJson<QVector<GetWhoIsJob::SessionInfo>>(jo.value("sessions"_ls));
-
-            return result;
+            fromJson(jo.value("sessions"_ls), result.sessions);
         }
     };
 } // namespace QMatrixClient
@@ -94,8 +80,8 @@ const QHash<QString, GetWhoIsJob::DeviceInfo>& GetWhoIsJob::devices() const
 BaseJob::Status GetWhoIsJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->userId = fromJson<QString>(json.value("user_id"_ls));
-    d->devices = fromJson<QHash<QString, DeviceInfo>>(json.value("devices"_ls));
+    fromJson(json.value("user_id"_ls), d->userId);
+    fromJson(json.value("devices"_ls), d->devices);
     return Success;
 }
 
diff --git a/lib/csapi/administrative_contact.cpp b/lib/csapi/administrative_contact.cpp
index f62002a6..9b021e17 100644
--- a/lib/csapi/administrative_contact.cpp
+++ b/lib/csapi/administrative_contact.cpp
@@ -16,21 +16,14 @@ namespace QMatrixClient
 {
     // Converters
 
-    template <> struct FromJsonObject<GetAccount3PIDsJob::ThirdPartyIdentifier>
+    template <> struct JsonObjectConverter<GetAccount3PIDsJob::ThirdPartyIdentifier>
     {
-        GetAccount3PIDsJob::ThirdPartyIdentifier operator()(const QJsonObject& jo) const
+        static void fillFrom(const QJsonObject& jo, GetAccount3PIDsJob::ThirdPartyIdentifier& result)
         {
-            GetAccount3PIDsJob::ThirdPartyIdentifier result;
-            result.medium =
-                fromJson<QString>(jo.value("medium"_ls));
-            result.address =
-                fromJson<QString>(jo.value("address"_ls));
-            result.validatedAt =
-                fromJson<qint64>(jo.value("validated_at"_ls));
-            result.addedAt =
-                fromJson<qint64>(jo.value("added_at"_ls));
-
-            return result;
+            fromJson(jo.value("medium"_ls), result.medium);
+            fromJson(jo.value("address"_ls), result.address);
+            fromJson(jo.value("validated_at"_ls), result.validatedAt);
+            fromJson(jo.value("added_at"_ls), result.addedAt);
         }
     };
 } // namespace QMatrixClient
@@ -66,7 +59,7 @@ const QVector<GetAccount3PIDsJob::ThirdPartyIdentifier>& GetAccount3PIDsJob::thr
 BaseJob::Status GetAccount3PIDsJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->threepids = fromJson<QVector<ThirdPartyIdentifier>>(json.value("threepids"_ls));
+    fromJson(json.value("threepids"_ls), d->threepids);
     return Success;
 }
 
@@ -74,14 +67,15 @@ namespace QMatrixClient
 {
     // Converters
 
-    QJsonObject toJson(const Post3PIDsJob::ThreePidCredentials& pod)
+    template <> struct JsonObjectConverter<Post3PIDsJob::ThreePidCredentials>
     {
-        QJsonObject jo;
-        addParam<>(jo, QStringLiteral("client_secret"), pod.clientSecret);
-        addParam<>(jo, QStringLiteral("id_server"), pod.idServer);
-        addParam<>(jo, QStringLiteral("sid"), pod.sid);
-        return jo;
-    }
+        static void dumpTo(QJsonObject& jo, const Post3PIDsJob::ThreePidCredentials& pod)
+        {
+            addParam<>(jo, QStringLiteral("client_secret"), pod.clientSecret);
+            addParam<>(jo, QStringLiteral("id_server"), pod.idServer);
+            addParam<>(jo, QStringLiteral("sid"), pod.sid);
+        }
+    };
 } // namespace QMatrixClient
 
 static const auto Post3PIDsJobName = QStringLiteral("Post3PIDsJob");
@@ -139,7 +133,7 @@ const Sid& RequestTokenTo3PIDEmailJob::data() const
 
 BaseJob::Status RequestTokenTo3PIDEmailJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<Sid>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
@@ -175,7 +169,7 @@ const Sid& RequestTokenTo3PIDMSISDNJob::data() const
 
 BaseJob::Status RequestTokenTo3PIDMSISDNJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<Sid>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
diff --git a/lib/csapi/content-repo.cpp b/lib/csapi/content-repo.cpp
index 9b590e42..22223985 100644
--- a/lib/csapi/content-repo.cpp
+++ b/lib/csapi/content-repo.cpp
@@ -52,7 +52,7 @@ BaseJob::Status UploadContentJob::parseJson(const QJsonDocument& data)
     if (!json.contains("content_uri"_ls))
         return { JsonParseError,
             "The key 'content_uri' not found in the response" };
-    d->contentUri = fromJson<QString>(json.value("content_uri"_ls));
+    fromJson(json.value("content_uri"_ls), d->contentUri);
     return Success;
 }
 
@@ -276,8 +276,8 @@ const QString& GetUrlPreviewJob::ogImage() const
 BaseJob::Status GetUrlPreviewJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->matrixImageSize = fromJson<qint64>(json.value("matrix:image:size"_ls));
-    d->ogImage = fromJson<QString>(json.value("og:image"_ls));
+    fromJson(json.value("matrix:image:size"_ls), d->matrixImageSize);
+    fromJson(json.value("og:image"_ls), d->ogImage);
     return Success;
 }
 
@@ -312,7 +312,7 @@ Omittable<qint64> GetConfigJob::uploadSize() const
 BaseJob::Status GetConfigJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->uploadSize = fromJson<qint64>(json.value("m.upload.size"_ls));
+    fromJson(json.value("m.upload.size"_ls), d->uploadSize);
     return Success;
 }
 
diff --git a/lib/csapi/create_room.cpp b/lib/csapi/create_room.cpp
index 36f83727..c44b73ac 100644
--- a/lib/csapi/create_room.cpp
+++ b/lib/csapi/create_room.cpp
@@ -16,23 +16,25 @@ namespace QMatrixClient
 {
     // Converters
 
-    QJsonObject toJson(const CreateRoomJob::Invite3pid& pod)
+    template <> struct JsonObjectConverter<CreateRoomJob::Invite3pid>
     {
-        QJsonObject jo;
-        addParam<>(jo, QStringLiteral("id_server"), pod.idServer);
-        addParam<>(jo, QStringLiteral("medium"), pod.medium);
-        addParam<>(jo, QStringLiteral("address"), pod.address);
-        return jo;
-    }
+        static void dumpTo(QJsonObject& jo, const CreateRoomJob::Invite3pid& pod)
+        {
+            addParam<>(jo, QStringLiteral("id_server"), pod.idServer);
+            addParam<>(jo, QStringLiteral("medium"), pod.medium);
+            addParam<>(jo, QStringLiteral("address"), pod.address);
+        }
+    };
 
-    QJsonObject toJson(const CreateRoomJob::StateEvent& pod)
+    template <> struct JsonObjectConverter<CreateRoomJob::StateEvent>
     {
-        QJsonObject jo;
-        addParam<>(jo, QStringLiteral("type"), pod.type);
-        addParam<IfNotEmpty>(jo, QStringLiteral("state_key"), pod.stateKey);
-        addParam<>(jo, QStringLiteral("content"), pod.content);
-        return jo;
-    }
+        static void dumpTo(QJsonObject& jo, const CreateRoomJob::StateEvent& pod)
+        {
+            addParam<>(jo, QStringLiteral("type"), pod.type);
+            addParam<IfNotEmpty>(jo, QStringLiteral("state_key"), pod.stateKey);
+            addParam<>(jo, QStringLiteral("content"), pod.content);
+        }
+    };
 } // namespace QMatrixClient
 
 class CreateRoomJob::Private
@@ -77,7 +79,7 @@ BaseJob::Status CreateRoomJob::parseJson(const QJsonDocument& data)
     if (!json.contains("room_id"_ls))
         return { JsonParseError,
             "The key 'room_id' not found in the response" };
-    d->roomId = fromJson<QString>(json.value("room_id"_ls));
+    fromJson(json.value("room_id"_ls), d->roomId);
     return Success;
 }
 
diff --git a/lib/csapi/definitions/auth_data.cpp b/lib/csapi/definitions/auth_data.cpp
index f8639432..006b8c7e 100644
--- a/lib/csapi/definitions/auth_data.cpp
+++ b/lib/csapi/definitions/auth_data.cpp
@@ -6,23 +6,20 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const AuthenticationData& pod)
+void JsonObjectConverter<AuthenticationData>::dumpTo(
+        QJsonObject& jo, const AuthenticationData& pod)
 {
-    QJsonObject jo = toJson(pod.authInfo);
+    fillJson(jo, pod.authInfo);
     addParam<>(jo, QStringLiteral("type"), pod.type);
     addParam<IfNotEmpty>(jo, QStringLiteral("session"), pod.session);
-    return jo;
 }
 
-AuthenticationData FromJsonObject<AuthenticationData>::operator()(QJsonObject jo) const
+void JsonObjectConverter<AuthenticationData>::fillFrom(
+    QJsonObject jo, AuthenticationData& result)
 {
-    AuthenticationData result;
-    result.type =
-        fromJson<QString>(jo.take("type"_ls));
-    result.session =
-        fromJson<QString>(jo.take("session"_ls));
+    fromJson(jo.take("type"_ls), result.type);
+    fromJson(jo.take("session"_ls), result.session);
 
-    result.authInfo = fromJson<QHash<QString, QJsonObject>>(jo);
-    return result;
+    fromJson(jo, result.authInfo);
 }
 
diff --git a/lib/csapi/definitions/auth_data.h b/lib/csapi/definitions/auth_data.h
index 661d3e5f..26eb205c 100644
--- a/lib/csapi/definitions/auth_data.h
+++ b/lib/csapi/definitions/auth_data.h
@@ -23,12 +23,10 @@ namespace QMatrixClient
         /// Keys dependent on the login type
         QHash<QString, QJsonObject> authInfo;
     };
-
-    QJsonObject toJson(const AuthenticationData& pod);
-
-    template <> struct FromJsonObject<AuthenticationData>
+    template <> struct JsonObjectConverter<AuthenticationData>
     {
-        AuthenticationData operator()(QJsonObject jo) const;
+        static void dumpTo(QJsonObject& jo, const AuthenticationData& pod);
+        static void fillFrom(QJsonObject jo, AuthenticationData& pod);
     };
 
 } // namespace QMatrixClient
diff --git a/lib/csapi/definitions/client_device.cpp b/lib/csapi/definitions/client_device.cpp
index 4a192f85..752b806a 100644
--- a/lib/csapi/definitions/client_device.cpp
+++ b/lib/csapi/definitions/client_device.cpp
@@ -6,28 +6,21 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const Device& pod)
+void JsonObjectConverter<Device>::dumpTo(
+        QJsonObject& jo, const Device& pod)
 {
-    QJsonObject jo;
     addParam<>(jo, QStringLiteral("device_id"), pod.deviceId);
     addParam<IfNotEmpty>(jo, QStringLiteral("display_name"), pod.displayName);
     addParam<IfNotEmpty>(jo, QStringLiteral("last_seen_ip"), pod.lastSeenIp);
     addParam<IfNotEmpty>(jo, QStringLiteral("last_seen_ts"), pod.lastSeenTs);
-    return jo;
 }
 
-Device FromJsonObject<Device>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<Device>::fillFrom(
+    const QJsonObject& jo, Device& result)
 {
-    Device result;
-    result.deviceId =
-        fromJson<QString>(jo.value("device_id"_ls));
-    result.displayName =
-        fromJson<QString>(jo.value("display_name"_ls));
-    result.lastSeenIp =
-        fromJson<QString>(jo.value("last_seen_ip"_ls));
-    result.lastSeenTs =
-        fromJson<qint64>(jo.value("last_seen_ts"_ls));
-
-    return result;
+    fromJson(jo.value("device_id"_ls), result.deviceId);
+    fromJson(jo.value("display_name"_ls), result.displayName);
+    fromJson(jo.value("last_seen_ip"_ls), result.lastSeenIp);
+    fromJson(jo.value("last_seen_ts"_ls), result.lastSeenTs);
 }
 
diff --git a/lib/csapi/definitions/client_device.h b/lib/csapi/definitions/client_device.h
index 9f10888a..a6224f71 100644
--- a/lib/csapi/definitions/client_device.h
+++ b/lib/csapi/definitions/client_device.h
@@ -28,12 +28,10 @@ namespace QMatrixClient
         /// reasons).
         Omittable<qint64> lastSeenTs;
     };
-
-    QJsonObject toJson(const Device& pod);
-
-    template <> struct FromJsonObject<Device>
+    template <> struct JsonObjectConverter<Device>
     {
-        Device operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const Device& pod);
+        static void fillFrom(const QJsonObject& jo, Device& pod);
     };
 
 } // namespace QMatrixClient
diff --git a/lib/csapi/definitions/device_keys.cpp b/lib/csapi/definitions/device_keys.cpp
index a0e0ca42..1e79499f 100644
--- a/lib/csapi/definitions/device_keys.cpp
+++ b/lib/csapi/definitions/device_keys.cpp
@@ -6,31 +6,23 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const DeviceKeys& pod)
+void JsonObjectConverter<DeviceKeys>::dumpTo(
+        QJsonObject& jo, const DeviceKeys& pod)
 {
-    QJsonObject jo;
     addParam<>(jo, QStringLiteral("user_id"), pod.userId);
     addParam<>(jo, QStringLiteral("device_id"), pod.deviceId);
     addParam<>(jo, QStringLiteral("algorithms"), pod.algorithms);
     addParam<>(jo, QStringLiteral("keys"), pod.keys);
     addParam<>(jo, QStringLiteral("signatures"), pod.signatures);
-    return jo;
 }
 
-DeviceKeys FromJsonObject<DeviceKeys>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<DeviceKeys>::fillFrom(
+    const QJsonObject& jo, DeviceKeys& result)
 {
-    DeviceKeys result;
-    result.userId =
-        fromJson<QString>(jo.value("user_id"_ls));
-    result.deviceId =
-        fromJson<QString>(jo.value("device_id"_ls));
-    result.algorithms =
-        fromJson<QStringList>(jo.value("algorithms"_ls));
-    result.keys =
-        fromJson<QHash<QString, QString>>(jo.value("keys"_ls));
-    result.signatures =
-        fromJson<QHash<QString, QHash<QString, QString>>>(jo.value("signatures"_ls));
-
-    return result;
+    fromJson(jo.value("user_id"_ls), result.userId);
+    fromJson(jo.value("device_id"_ls), result.deviceId);
+    fromJson(jo.value("algorithms"_ls), result.algorithms);
+    fromJson(jo.value("keys"_ls), result.keys);
+    fromJson(jo.value("signatures"_ls), result.signatures);
 }
 
diff --git a/lib/csapi/definitions/device_keys.h b/lib/csapi/definitions/device_keys.h
index 6023e7e8..8ebe1125 100644
--- a/lib/csapi/definitions/device_keys.h
+++ b/lib/csapi/definitions/device_keys.h
@@ -34,12 +34,10 @@ namespace QMatrixClient
         /// JSON`_.
         QHash<QString, QHash<QString, QString>> signatures;
     };
-
-    QJsonObject toJson(const DeviceKeys& pod);
-
-    template <> struct FromJsonObject<DeviceKeys>
+    template <> struct JsonObjectConverter<DeviceKeys>
     {
-        DeviceKeys operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const DeviceKeys& pod);
+        static void fillFrom(const QJsonObject& jo, DeviceKeys& pod);
     };
 
 } // namespace QMatrixClient
diff --git a/lib/csapi/definitions/event_filter.cpp b/lib/csapi/definitions/event_filter.cpp
index cc444db0..b20d7807 100644
--- a/lib/csapi/definitions/event_filter.cpp
+++ b/lib/csapi/definitions/event_filter.cpp
@@ -6,31 +6,23 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const EventFilter& pod)
+void JsonObjectConverter<EventFilter>::dumpTo(
+        QJsonObject& jo, const EventFilter& pod)
 {
-    QJsonObject jo;
     addParam<IfNotEmpty>(jo, QStringLiteral("limit"), pod.limit);
     addParam<IfNotEmpty>(jo, QStringLiteral("not_senders"), pod.notSenders);
     addParam<IfNotEmpty>(jo, QStringLiteral("not_types"), pod.notTypes);
     addParam<IfNotEmpty>(jo, QStringLiteral("senders"), pod.senders);
     addParam<IfNotEmpty>(jo, QStringLiteral("types"), pod.types);
-    return jo;
 }
 
-EventFilter FromJsonObject<EventFilter>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<EventFilter>::fillFrom(
+    const QJsonObject& jo, EventFilter& result)
 {
-    EventFilter result;
-    result.limit =
-        fromJson<int>(jo.value("limit"_ls));
-    result.notSenders =
-        fromJson<QStringList>(jo.value("not_senders"_ls));
-    result.notTypes =
-        fromJson<QStringList>(jo.value("not_types"_ls));
-    result.senders =
-        fromJson<QStringList>(jo.value("senders"_ls));
-    result.types =
-        fromJson<QStringList>(jo.value("types"_ls));
-
-    return result;
+    fromJson(jo.value("limit"_ls), result.limit);
+    fromJson(jo.value("not_senders"_ls), result.notSenders);
+    fromJson(jo.value("not_types"_ls), result.notTypes);
+    fromJson(jo.value("senders"_ls), result.senders);
+    fromJson(jo.value("types"_ls), result.types);
 }
 
diff --git a/lib/csapi/definitions/event_filter.h b/lib/csapi/definitions/event_filter.h
index 5c6a5b27..6de1fe79 100644
--- a/lib/csapi/definitions/event_filter.h
+++ b/lib/csapi/definitions/event_filter.h
@@ -25,12 +25,10 @@ namespace QMatrixClient
         /// A list of event types to include. If this list is absent then all event types are included. A ``'*'`` can be used as a wildcard to match any sequence of characters.
         QStringList types;
     };
-
-    QJsonObject toJson(const EventFilter& pod);
-
-    template <> struct FromJsonObject<EventFilter>
+    template <> struct JsonObjectConverter<EventFilter>
     {
-        EventFilter operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const EventFilter& pod);
+        static void fillFrom(const QJsonObject& jo, EventFilter& pod);
     };
 
 } // namespace QMatrixClient
diff --git a/lib/csapi/definitions/public_rooms_response.cpp b/lib/csapi/definitions/public_rooms_response.cpp
index 2f52501d..0d26662c 100644
--- a/lib/csapi/definitions/public_rooms_response.cpp
+++ b/lib/csapi/definitions/public_rooms_response.cpp
@@ -6,9 +6,9 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const PublicRoomsChunk& pod)
+void JsonObjectConverter<PublicRoomsChunk>::dumpTo(
+        QJsonObject& jo, const PublicRoomsChunk& pod)
 {
-    QJsonObject jo;
     addParam<IfNotEmpty>(jo, QStringLiteral("aliases"), pod.aliases);
     addParam<IfNotEmpty>(jo, QStringLiteral("canonical_alias"), pod.canonicalAlias);
     addParam<IfNotEmpty>(jo, QStringLiteral("name"), pod.name);
@@ -18,56 +18,37 @@ QJsonObject QMatrixClient::toJson(const PublicRoomsChunk& pod)
     addParam<>(jo, QStringLiteral("world_readable"), pod.worldReadable);
     addParam<>(jo, QStringLiteral("guest_can_join"), pod.guestCanJoin);
     addParam<IfNotEmpty>(jo, QStringLiteral("avatar_url"), pod.avatarUrl);
-    return jo;
 }
 
-PublicRoomsChunk FromJsonObject<PublicRoomsChunk>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<PublicRoomsChunk>::fillFrom(
+    const QJsonObject& jo, PublicRoomsChunk& result)
 {
-    PublicRoomsChunk result;
-    result.aliases =
-        fromJson<QStringList>(jo.value("aliases"_ls));
-    result.canonicalAlias =
-        fromJson<QString>(jo.value("canonical_alias"_ls));
-    result.name =
-        fromJson<QString>(jo.value("name"_ls));
-    result.numJoinedMembers =
-        fromJson<int>(jo.value("num_joined_members"_ls));
-    result.roomId =
-        fromJson<QString>(jo.value("room_id"_ls));
-    result.topic =
-        fromJson<QString>(jo.value("topic"_ls));
-    result.worldReadable =
-        fromJson<bool>(jo.value("world_readable"_ls));
-    result.guestCanJoin =
-        fromJson<bool>(jo.value("guest_can_join"_ls));
-    result.avatarUrl =
-        fromJson<QString>(jo.value("avatar_url"_ls));
-
-    return result;
+    fromJson(jo.value("aliases"_ls), result.aliases);
+    fromJson(jo.value("canonical_alias"_ls), result.canonicalAlias);
+    fromJson(jo.value("name"_ls), result.name);
+    fromJson(jo.value("num_joined_members"_ls), result.numJoinedMembers);
+    fromJson(jo.value("room_id"_ls), result.roomId);
+    fromJson(jo.value("topic"_ls), result.topic);
+    fromJson(jo.value("world_readable"_ls), result.worldReadable);
+    fromJson(jo.value("guest_can_join"_ls), result.guestCanJoin);
+    fromJson(jo.value("avatar_url"_ls), result.avatarUrl);
 }
 
-QJsonObject QMatrixClient::toJson(const PublicRoomsResponse& pod)
+void JsonObjectConverter<PublicRoomsResponse>::dumpTo(
+        QJsonObject& jo, const PublicRoomsResponse& pod)
 {
-    QJsonObject jo;
     addParam<>(jo, QStringLiteral("chunk"), pod.chunk);
     addParam<IfNotEmpty>(jo, QStringLiteral("next_batch"), pod.nextBatch);
     addParam<IfNotEmpty>(jo, QStringLiteral("prev_batch"), pod.prevBatch);
     addParam<IfNotEmpty>(jo, QStringLiteral("total_room_count_estimate"), pod.totalRoomCountEstimate);
-    return jo;
 }
 
-PublicRoomsResponse FromJsonObject<PublicRoomsResponse>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<PublicRoomsResponse>::fillFrom(
+    const QJsonObject& jo, PublicRoomsResponse& result)
 {
-    PublicRoomsResponse result;
-    result.chunk =
-        fromJson<QVector<PublicRoomsChunk>>(jo.value("chunk"_ls));
-    result.nextBatch =
-        fromJson<QString>(jo.value("next_batch"_ls));
-    result.prevBatch =
-        fromJson<QString>(jo.value("prev_batch"_ls));
-    result.totalRoomCountEstimate =
-        fromJson<int>(jo.value("total_room_count_estimate"_ls));
-
-    return result;
+    fromJson(jo.value("chunk"_ls), result.chunk);
+    fromJson(jo.value("next_batch"_ls), result.nextBatch);
+    fromJson(jo.value("prev_batch"_ls), result.prevBatch);
+    fromJson(jo.value("total_room_count_estimate"_ls), result.totalRoomCountEstimate);
 }
 
diff --git a/lib/csapi/definitions/public_rooms_response.h b/lib/csapi/definitions/public_rooms_response.h
index 88c805ba..4c54ac25 100644
--- a/lib/csapi/definitions/public_rooms_response.h
+++ b/lib/csapi/definitions/public_rooms_response.h
@@ -36,12 +36,10 @@ namespace QMatrixClient
         /// The URL for the room's avatar, if one is set.
         QString avatarUrl;
     };
-
-    QJsonObject toJson(const PublicRoomsChunk& pod);
-
-    template <> struct FromJsonObject<PublicRoomsChunk>
+    template <> struct JsonObjectConverter<PublicRoomsChunk>
     {
-        PublicRoomsChunk operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const PublicRoomsChunk& pod);
+        static void fillFrom(const QJsonObject& jo, PublicRoomsChunk& pod);
     };
 
     /// A list of the rooms on the server.
@@ -61,12 +59,10 @@ namespace QMatrixClient
         /// server has an estimate.
         Omittable<int> totalRoomCountEstimate;
     };
-
-    QJsonObject toJson(const PublicRoomsResponse& pod);
-
-    template <> struct FromJsonObject<PublicRoomsResponse>
+    template <> struct JsonObjectConverter<PublicRoomsResponse>
     {
-        PublicRoomsResponse operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const PublicRoomsResponse& pod);
+        static void fillFrom(const QJsonObject& jo, PublicRoomsResponse& pod);
     };
 
 } // namespace QMatrixClient
diff --git a/lib/csapi/definitions/push_condition.cpp b/lib/csapi/definitions/push_condition.cpp
index 045094bc..ace02755 100644
--- a/lib/csapi/definitions/push_condition.cpp
+++ b/lib/csapi/definitions/push_condition.cpp
@@ -6,28 +6,21 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const PushCondition& pod)
+void JsonObjectConverter<PushCondition>::dumpTo(
+        QJsonObject& jo, const PushCondition& pod)
 {
-    QJsonObject jo;
     addParam<>(jo, QStringLiteral("kind"), pod.kind);
     addParam<IfNotEmpty>(jo, QStringLiteral("key"), pod.key);
     addParam<IfNotEmpty>(jo, QStringLiteral("pattern"), pod.pattern);
     addParam<IfNotEmpty>(jo, QStringLiteral("is"), pod.is);
-    return jo;
 }
 
-PushCondition FromJsonObject<PushCondition>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<PushCondition>::fillFrom(
+    const QJsonObject& jo, PushCondition& result)
 {
-    PushCondition result;
-    result.kind =
-        fromJson<QString>(jo.value("kind"_ls));
-    result.key =
-        fromJson<QString>(jo.value("key"_ls));
-    result.pattern =
-        fromJson<QString>(jo.value("pattern"_ls));
-    result.is =
-        fromJson<QString>(jo.value("is"_ls));
-
-    return result;
+    fromJson(jo.value("kind"_ls), result.kind);
+    fromJson(jo.value("key"_ls), result.key);
+    fromJson(jo.value("pattern"_ls), result.pattern);
+    fromJson(jo.value("is"_ls), result.is);
 }
 
diff --git a/lib/csapi/definitions/push_condition.h b/lib/csapi/definitions/push_condition.h
index defcebb3..e45526d2 100644
--- a/lib/csapi/definitions/push_condition.h
+++ b/lib/csapi/definitions/push_condition.h
@@ -28,12 +28,10 @@ namespace QMatrixClient
         /// so forth. If no prefix is present, this parameter defaults to ==.
         QString is;
     };
-
-    QJsonObject toJson(const PushCondition& pod);
-
-    template <> struct FromJsonObject<PushCondition>
+    template <> struct JsonObjectConverter<PushCondition>
     {
-        PushCondition operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const PushCondition& pod);
+        static void fillFrom(const QJsonObject& jo, PushCondition& pod);
     };
 
 } // namespace QMatrixClient
diff --git a/lib/csapi/definitions/push_rule.cpp b/lib/csapi/definitions/push_rule.cpp
index baddd187..abbb04b5 100644
--- a/lib/csapi/definitions/push_rule.cpp
+++ b/lib/csapi/definitions/push_rule.cpp
@@ -6,34 +6,25 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const PushRule& pod)
+void JsonObjectConverter<PushRule>::dumpTo(
+        QJsonObject& jo, const PushRule& pod)
 {
-    QJsonObject jo;
     addParam<>(jo, QStringLiteral("actions"), pod.actions);
     addParam<>(jo, QStringLiteral("default"), pod.isDefault);
     addParam<>(jo, QStringLiteral("enabled"), pod.enabled);
     addParam<>(jo, QStringLiteral("rule_id"), pod.ruleId);
     addParam<IfNotEmpty>(jo, QStringLiteral("conditions"), pod.conditions);
     addParam<IfNotEmpty>(jo, QStringLiteral("pattern"), pod.pattern);
-    return jo;
 }
 
-PushRule FromJsonObject<PushRule>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<PushRule>::fillFrom(
+    const QJsonObject& jo, PushRule& result)
 {
-    PushRule result;
-    result.actions =
-        fromJson<QVector<QVariant>>(jo.value("actions"_ls));
-    result.isDefault =
-        fromJson<bool>(jo.value("default"_ls));
-    result.enabled =
-        fromJson<bool>(jo.value("enabled"_ls));
-    result.ruleId =
-        fromJson<QString>(jo.value("rule_id"_ls));
-    result.conditions =
-        fromJson<QVector<PushCondition>>(jo.value("conditions"_ls));
-    result.pattern =
-        fromJson<QString>(jo.value("pattern"_ls));
-
-    return result;
+    fromJson(jo.value("actions"_ls), result.actions);
+    fromJson(jo.value("default"_ls), result.isDefault);
+    fromJson(jo.value("enabled"_ls), result.enabled);
+    fromJson(jo.value("rule_id"_ls), result.ruleId);
+    fromJson(jo.value("conditions"_ls), result.conditions);
+    fromJson(jo.value("pattern"_ls), result.pattern);
 }
 
diff --git a/lib/csapi/definitions/push_rule.h b/lib/csapi/definitions/push_rule.h
index 5f52876d..05328b8b 100644
--- a/lib/csapi/definitions/push_rule.h
+++ b/lib/csapi/definitions/push_rule.h
@@ -34,12 +34,10 @@ namespace QMatrixClient
         /// rules.
         QString pattern;
     };
-
-    QJsonObject toJson(const PushRule& pod);
-
-    template <> struct FromJsonObject<PushRule>
+    template <> struct JsonObjectConverter<PushRule>
     {
-        PushRule operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const PushRule& pod);
+        static void fillFrom(const QJsonObject& jo, PushRule& pod);
     };
 
 } // namespace QMatrixClient
diff --git a/lib/csapi/definitions/push_ruleset.cpp b/lib/csapi/definitions/push_ruleset.cpp
index 14b7a4b6..f1bad882 100644
--- a/lib/csapi/definitions/push_ruleset.cpp
+++ b/lib/csapi/definitions/push_ruleset.cpp
@@ -6,31 +6,23 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const PushRuleset& pod)
+void JsonObjectConverter<PushRuleset>::dumpTo(
+        QJsonObject& jo, const PushRuleset& pod)
 {
-    QJsonObject jo;
     addParam<IfNotEmpty>(jo, QStringLiteral("content"), pod.content);
     addParam<IfNotEmpty>(jo, QStringLiteral("override"), pod.override);
     addParam<IfNotEmpty>(jo, QStringLiteral("room"), pod.room);
     addParam<IfNotEmpty>(jo, QStringLiteral("sender"), pod.sender);
     addParam<IfNotEmpty>(jo, QStringLiteral("underride"), pod.underride);
-    return jo;
 }
 
-PushRuleset FromJsonObject<PushRuleset>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<PushRuleset>::fillFrom(
+    const QJsonObject& jo, PushRuleset& result)
 {
-    PushRuleset result;
-    result.content =
-        fromJson<QVector<PushRule>>(jo.value("content"_ls));
-    result.override =
-        fromJson<QVector<PushRule>>(jo.value("override"_ls));
-    result.room =
-        fromJson<QVector<PushRule>>(jo.value("room"_ls));
-    result.sender =
-        fromJson<QVector<PushRule>>(jo.value("sender"_ls));
-    result.underride =
-        fromJson<QVector<PushRule>>(jo.value("underride"_ls));
-
-    return result;
+    fromJson(jo.value("content"_ls), result.content);
+    fromJson(jo.value("override"_ls), result.override);
+    fromJson(jo.value("room"_ls), result.room);
+    fromJson(jo.value("sender"_ls), result.sender);
+    fromJson(jo.value("underride"_ls), result.underride);
 }
 
diff --git a/lib/csapi/definitions/push_ruleset.h b/lib/csapi/definitions/push_ruleset.h
index a274b72a..f2d937c0 100644
--- a/lib/csapi/definitions/push_ruleset.h
+++ b/lib/csapi/definitions/push_ruleset.h
@@ -22,12 +22,10 @@ namespace QMatrixClient
         QVector<PushRule> sender;
         QVector<PushRule> underride;
     };
-
-    QJsonObject toJson(const PushRuleset& pod);
-
-    template <> struct FromJsonObject<PushRuleset>
+    template <> struct JsonObjectConverter<PushRuleset>
     {
-        PushRuleset operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const PushRuleset& pod);
+        static void fillFrom(const QJsonObject& jo, PushRuleset& pod);
     };
 
 } // namespace QMatrixClient
diff --git a/lib/csapi/definitions/room_event_filter.cpp b/lib/csapi/definitions/room_event_filter.cpp
index 8cd2ded7..df92e684 100644
--- a/lib/csapi/definitions/room_event_filter.cpp
+++ b/lib/csapi/definitions/room_event_filter.cpp
@@ -6,31 +6,21 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const RoomEventFilter& pod)
+void JsonObjectConverter<RoomEventFilter>::dumpTo(
+        QJsonObject& jo, const RoomEventFilter& pod)
 {
-    QJsonObject jo;
+    fillJson<EventFilter>(jo, pod);
     addParam<IfNotEmpty>(jo, QStringLiteral("not_rooms"), pod.notRooms);
     addParam<IfNotEmpty>(jo, QStringLiteral("rooms"), pod.rooms);
     addParam<IfNotEmpty>(jo, QStringLiteral("contains_url"), pod.containsUrl);
-    addParam<IfNotEmpty>(jo, QStringLiteral("lazy_load_members"), pod.lazyLoadMembers);
-    addParam<IfNotEmpty>(jo, QStringLiteral("include_redundant_members"), pod.includeRedundantMembers);
-    return jo;
 }
 
-RoomEventFilter FromJsonObject<RoomEventFilter>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<RoomEventFilter>::fillFrom(
+    const QJsonObject& jo, RoomEventFilter& result)
 {
-    RoomEventFilter result;
-    result.notRooms =
-        fromJson<QStringList>(jo.value("not_rooms"_ls));
-    result.rooms =
-        fromJson<QStringList>(jo.value("rooms"_ls));
-    result.containsUrl =
-        fromJson<bool>(jo.value("contains_url"_ls));
-    result.lazyLoadMembers =
-        fromJson<bool>(jo.value("lazy_load_members"_ls));
-    result.includeRedundantMembers =
-        fromJson<bool>(jo.value("include_redundant_members"_ls));
-
-    return result;
+    fillFromJson<EventFilter>(jo, result);
+    fromJson(jo.value("not_rooms"_ls), result.notRooms);
+    fromJson(jo.value("rooms"_ls), result.rooms);
+    fromJson(jo.value("contains_url"_ls), result.containsUrl);
 }
 
diff --git a/lib/csapi/definitions/room_event_filter.h b/lib/csapi/definitions/room_event_filter.h
index 87f01189..3908b8ec 100644
--- a/lib/csapi/definitions/room_event_filter.h
+++ b/lib/csapi/definitions/room_event_filter.h
@@ -21,17 +21,11 @@ namespace QMatrixClient
         QStringList rooms;
         /// If ``true``, includes only events with a ``url`` key in their content. If ``false``, excludes those events. Defaults to ``false``.
         bool containsUrl;
-        /// If ``true``, the only ``m.room.member`` events returned in the ``state`` section of the ``/sync`` response are those which are definitely necessary for a client to display the ``sender`` of the timeline events in that response.  If ``false``, ``m.room.member`` events are not filtered.  By default, servers should suppress duplicate redundant lazy-loaded ``m.room.member`` events from being sent to a given client across multiple calls to ``/sync``, given that most clients cache membership events (see include_redundant_members to change this behaviour).
-        bool lazyLoadMembers;
-        /// If ``true``, the ``state`` section of the ``/sync`` response will always contain the ``m.room.member`` events required to display the ``sender`` of the timeline events in that response, assuming ``lazy_load_members`` is enabled. This means that redundant duplicate member events may be returned across multiple calls to ``/sync``. This is useful for naive clients who never track membership data. If ``false``, duplicate ``m.room.member`` events may be suppressed by the server across multiple calls to ``/sync``.  If ``lazy_load_members`` is ``false`` this field is ignored.
-        bool includeRedundantMembers;
     };
-
-    QJsonObject toJson(const RoomEventFilter& pod);
-
-    template <> struct FromJsonObject<RoomEventFilter>
+    template <> struct JsonObjectConverter<RoomEventFilter>
     {
-        RoomEventFilter operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const RoomEventFilter& pod);
+        static void fillFrom(const QJsonObject& jo, RoomEventFilter& pod);
     };
 
 } // namespace QMatrixClient
diff --git a/lib/csapi/definitions/sync_filter.cpp b/lib/csapi/definitions/sync_filter.cpp
index bd87804c..32752d1f 100644
--- a/lib/csapi/definitions/sync_filter.cpp
+++ b/lib/csapi/definitions/sync_filter.cpp
@@ -6,9 +6,25 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const RoomFilter& pod)
+void JsonObjectConverter<StateFilter>::dumpTo(
+        QJsonObject& jo, const StateFilter& pod)
+{
+    fillJson<RoomEventFilter>(jo, pod);
+    addParam<IfNotEmpty>(jo, QStringLiteral("lazy_load_members"), pod.lazyLoadMembers);
+    addParam<IfNotEmpty>(jo, QStringLiteral("include_redundant_members"), pod.includeRedundantMembers);
+}
+
+void JsonObjectConverter<StateFilter>::fillFrom(
+    const QJsonObject& jo, StateFilter& result)
+{
+    fillFromJson<RoomEventFilter>(jo, result);
+    fromJson(jo.value("lazy_load_members"_ls), result.lazyLoadMembers);
+    fromJson(jo.value("include_redundant_members"_ls), result.includeRedundantMembers);
+}
+
+void JsonObjectConverter<RoomFilter>::dumpTo(
+        QJsonObject& jo, const RoomFilter& pod)
 {
-    QJsonObject jo;
     addParam<IfNotEmpty>(jo, QStringLiteral("not_rooms"), pod.notRooms);
     addParam<IfNotEmpty>(jo, QStringLiteral("rooms"), pod.rooms);
     addParam<IfNotEmpty>(jo, QStringLiteral("ephemeral"), pod.ephemeral);
@@ -16,55 +32,37 @@ QJsonObject QMatrixClient::toJson(const RoomFilter& pod)
     addParam<IfNotEmpty>(jo, QStringLiteral("state"), pod.state);
     addParam<IfNotEmpty>(jo, QStringLiteral("timeline"), pod.timeline);
     addParam<IfNotEmpty>(jo, QStringLiteral("account_data"), pod.accountData);
-    return jo;
 }
 
-RoomFilter FromJsonObject<RoomFilter>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<RoomFilter>::fillFrom(
+    const QJsonObject& jo, RoomFilter& result)
 {
-    RoomFilter result;
-    result.notRooms =
-        fromJson<QStringList>(jo.value("not_rooms"_ls));
-    result.rooms =
-        fromJson<QStringList>(jo.value("rooms"_ls));
-    result.ephemeral =
-        fromJson<RoomEventFilter>(jo.value("ephemeral"_ls));
-    result.includeLeave =
-        fromJson<bool>(jo.value("include_leave"_ls));
-    result.state =
-        fromJson<RoomEventFilter>(jo.value("state"_ls));
-    result.timeline =
-        fromJson<RoomEventFilter>(jo.value("timeline"_ls));
-    result.accountData =
-        fromJson<RoomEventFilter>(jo.value("account_data"_ls));
-
-    return result;
+    fromJson(jo.value("not_rooms"_ls), result.notRooms);
+    fromJson(jo.value("rooms"_ls), result.rooms);
+    fromJson(jo.value("ephemeral"_ls), result.ephemeral);
+    fromJson(jo.value("include_leave"_ls), result.includeLeave);
+    fromJson(jo.value("state"_ls), result.state);
+    fromJson(jo.value("timeline"_ls), result.timeline);
+    fromJson(jo.value("account_data"_ls), result.accountData);
 }
 
-QJsonObject QMatrixClient::toJson(const Filter& pod)
+void JsonObjectConverter<Filter>::dumpTo(
+        QJsonObject& jo, const Filter& pod)
 {
-    QJsonObject jo;
     addParam<IfNotEmpty>(jo, QStringLiteral("event_fields"), pod.eventFields);
     addParam<IfNotEmpty>(jo, QStringLiteral("event_format"), pod.eventFormat);
     addParam<IfNotEmpty>(jo, QStringLiteral("presence"), pod.presence);
     addParam<IfNotEmpty>(jo, QStringLiteral("account_data"), pod.accountData);
     addParam<IfNotEmpty>(jo, QStringLiteral("room"), pod.room);
-    return jo;
 }
 
-Filter FromJsonObject<Filter>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<Filter>::fillFrom(
+    const QJsonObject& jo, Filter& result)
 {
-    Filter result;
-    result.eventFields =
-        fromJson<QStringList>(jo.value("event_fields"_ls));
-    result.eventFormat =
-        fromJson<QString>(jo.value("event_format"_ls));
-    result.presence =
-        fromJson<EventFilter>(jo.value("presence"_ls));
-    result.accountData =
-        fromJson<EventFilter>(jo.value("account_data"_ls));
-    result.room =
-        fromJson<RoomFilter>(jo.value("room"_ls));
-
-    return result;
+    fromJson(jo.value("event_fields"_ls), result.eventFields);
+    fromJson(jo.value("event_format"_ls), result.eventFormat);
+    fromJson(jo.value("presence"_ls), result.presence);
+    fromJson(jo.value("account_data"_ls), result.accountData);
+    fromJson(jo.value("room"_ls), result.room);
 }
 
diff --git a/lib/csapi/definitions/sync_filter.h b/lib/csapi/definitions/sync_filter.h
index ca275a9a..ccc3061b 100644
--- a/lib/csapi/definitions/sync_filter.h
+++ b/lib/csapi/definitions/sync_filter.h
@@ -14,6 +14,37 @@ namespace QMatrixClient
 {
     // Data structures
 
+    /// The state events to include for rooms.
+    struct StateFilter : RoomEventFilter
+    {
+        /// If ``true``, the only ``m.room.member`` events returned in
+        /// the ``state`` section of the ``/sync`` response are those
+        /// which are definitely necessary for a client to display
+        /// the ``sender`` of the timeline events in that response.
+        /// If ``false``, ``m.room.member`` events are not filtered.
+        /// By default, servers should suppress duplicate redundant
+        /// lazy-loaded ``m.room.member`` events from being sent to a given
+        /// client across multiple calls to ``/sync``, given that most clients
+        /// cache membership events (see ``include_redundant_members``
+        /// to change this behaviour).
+        bool lazyLoadMembers;
+        /// If ``true``, the ``state`` section of the ``/sync`` response will
+        /// always contain the ``m.room.member`` events required to display
+        /// the ``sender`` of the timeline events in that response, assuming
+        /// ``lazy_load_members`` is enabled. This means that redundant
+        /// duplicate member events may be returned across multiple calls to
+        /// ``/sync``. This is useful for naive clients who never track
+        /// membership data. If ``false``, duplicate ``m.room.member`` events
+        /// may be suppressed by the server across multiple calls to ``/sync``.
+        /// If ``lazy_load_members`` is ``false`` this field is ignored.
+        bool includeRedundantMembers;
+    };
+    template <> struct JsonObjectConverter<StateFilter>
+    {
+        static void dumpTo(QJsonObject& jo, const StateFilter& pod);
+        static void fillFrom(const QJsonObject& jo, StateFilter& pod);
+    };
+
     /// Filters to be applied to room data.
     struct RoomFilter
     {
@@ -26,18 +57,16 @@ namespace QMatrixClient
         /// Include rooms that the user has left in the sync, default false
         bool includeLeave;
         /// The state events to include for rooms.
-        Omittable<RoomEventFilter> state;
+        Omittable<StateFilter> state;
         /// The message and state update events to include for rooms.
         Omittable<RoomEventFilter> timeline;
         /// The per user account data to include for rooms.
         Omittable<RoomEventFilter> accountData;
     };
-
-    QJsonObject toJson(const RoomFilter& pod);
-
-    template <> struct FromJsonObject<RoomFilter>
+    template <> struct JsonObjectConverter<RoomFilter>
     {
-        RoomFilter operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const RoomFilter& pod);
+        static void fillFrom(const QJsonObject& jo, RoomFilter& pod);
     };
 
     struct Filter
@@ -53,12 +82,10 @@ namespace QMatrixClient
         /// Filters to be applied to room data.
         Omittable<RoomFilter> room;
     };
-
-    QJsonObject toJson(const Filter& pod);
-
-    template <> struct FromJsonObject<Filter>
+    template <> struct JsonObjectConverter<Filter>
     {
-        Filter operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const Filter& pod);
+        static void fillFrom(const QJsonObject& jo, Filter& pod);
     };
 
 } // namespace QMatrixClient
diff --git a/lib/csapi/definitions/user_identifier.cpp b/lib/csapi/definitions/user_identifier.cpp
index 80a6d450..05a27c1c 100644
--- a/lib/csapi/definitions/user_identifier.cpp
+++ b/lib/csapi/definitions/user_identifier.cpp
@@ -6,20 +6,18 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const UserIdentifier& pod)
+void JsonObjectConverter<UserIdentifier>::dumpTo(
+        QJsonObject& jo, const UserIdentifier& pod)
 {
-    QJsonObject jo = toJson(pod.additionalProperties);
+    fillJson(jo, pod.additionalProperties);
     addParam<>(jo, QStringLiteral("type"), pod.type);
-    return jo;
 }
 
-UserIdentifier FromJsonObject<UserIdentifier>::operator()(QJsonObject jo) const
+void JsonObjectConverter<UserIdentifier>::fillFrom(
+    QJsonObject jo, UserIdentifier& result)
 {
-    UserIdentifier result;
-    result.type =
-        fromJson<QString>(jo.take("type"_ls));
+    fromJson(jo.take("type"_ls), result.type);
 
-    result.additionalProperties = fromJson<QVariantHash>(jo);
-    return result;
+    fromJson(jo, result.additionalProperties);
 }
 
diff --git a/lib/csapi/definitions/user_identifier.h b/lib/csapi/definitions/user_identifier.h
index 42614436..cbb1550f 100644
--- a/lib/csapi/definitions/user_identifier.h
+++ b/lib/csapi/definitions/user_identifier.h
@@ -20,12 +20,10 @@ namespace QMatrixClient
         /// Identification information for a user
         QVariantHash additionalProperties;
     };
-
-    QJsonObject toJson(const UserIdentifier& pod);
-
-    template <> struct FromJsonObject<UserIdentifier>
+    template <> struct JsonObjectConverter<UserIdentifier>
     {
-        UserIdentifier operator()(QJsonObject jo) const;
+        static void dumpTo(QJsonObject& jo, const UserIdentifier& pod);
+        static void fillFrom(QJsonObject jo, UserIdentifier& pod);
     };
 
 } // namespace QMatrixClient
diff --git a/lib/csapi/definitions/wellknown/homeserver.cpp b/lib/csapi/definitions/wellknown/homeserver.cpp
index f1482ee4..0783f11b 100644
--- a/lib/csapi/definitions/wellknown/homeserver.cpp
+++ b/lib/csapi/definitions/wellknown/homeserver.cpp
@@ -6,19 +6,15 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const HomeserverInformation& pod)
+void JsonObjectConverter<HomeserverInformation>::dumpTo(
+        QJsonObject& jo, const HomeserverInformation& pod)
 {
-    QJsonObject jo;
     addParam<>(jo, QStringLiteral("base_url"), pod.baseUrl);
-    return jo;
 }
 
-HomeserverInformation FromJsonObject<HomeserverInformation>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<HomeserverInformation>::fillFrom(
+    const QJsonObject& jo, HomeserverInformation& result)
 {
-    HomeserverInformation result;
-    result.baseUrl =
-        fromJson<QString>(jo.value("base_url"_ls));
-
-    return result;
+    fromJson(jo.value("base_url"_ls), result.baseUrl);
 }
 
diff --git a/lib/csapi/definitions/wellknown/homeserver.h b/lib/csapi/definitions/wellknown/homeserver.h
index 09d6ba63..f6761c30 100644
--- a/lib/csapi/definitions/wellknown/homeserver.h
+++ b/lib/csapi/definitions/wellknown/homeserver.h
@@ -17,12 +17,10 @@ namespace QMatrixClient
         /// The base URL for the homeserver for client-server connections.
         QString baseUrl;
     };
-
-    QJsonObject toJson(const HomeserverInformation& pod);
-
-    template <> struct FromJsonObject<HomeserverInformation>
+    template <> struct JsonObjectConverter<HomeserverInformation>
     {
-        HomeserverInformation operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const HomeserverInformation& pod);
+        static void fillFrom(const QJsonObject& jo, HomeserverInformation& pod);
     };
 
 } // namespace QMatrixClient
diff --git a/lib/csapi/definitions/wellknown/identity_server.cpp b/lib/csapi/definitions/wellknown/identity_server.cpp
index f9d7bc37..99f36641 100644
--- a/lib/csapi/definitions/wellknown/identity_server.cpp
+++ b/lib/csapi/definitions/wellknown/identity_server.cpp
@@ -6,19 +6,15 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const IdentityServerInformation& pod)
+void JsonObjectConverter<IdentityServerInformation>::dumpTo(
+        QJsonObject& jo, const IdentityServerInformation& pod)
 {
-    QJsonObject jo;
     addParam<>(jo, QStringLiteral("base_url"), pod.baseUrl);
-    return jo;
 }
 
-IdentityServerInformation FromJsonObject<IdentityServerInformation>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<IdentityServerInformation>::fillFrom(
+    const QJsonObject& jo, IdentityServerInformation& result)
 {
-    IdentityServerInformation result;
-    result.baseUrl =
-        fromJson<QString>(jo.value("base_url"_ls));
-
-    return result;
+    fromJson(jo.value("base_url"_ls), result.baseUrl);
 }
 
diff --git a/lib/csapi/definitions/wellknown/identity_server.h b/lib/csapi/definitions/wellknown/identity_server.h
index cb8ffcee..67d8b08d 100644
--- a/lib/csapi/definitions/wellknown/identity_server.h
+++ b/lib/csapi/definitions/wellknown/identity_server.h
@@ -17,12 +17,10 @@ namespace QMatrixClient
         /// The base URL for the identity server for client-server connections.
         QString baseUrl;
     };
-
-    QJsonObject toJson(const IdentityServerInformation& pod);
-
-    template <> struct FromJsonObject<IdentityServerInformation>
+    template <> struct JsonObjectConverter<IdentityServerInformation>
     {
-        IdentityServerInformation operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const IdentityServerInformation& pod);
+        static void fillFrom(const QJsonObject& jo, IdentityServerInformation& pod);
     };
 
 } // namespace QMatrixClient
diff --git a/lib/csapi/device_management.cpp b/lib/csapi/device_management.cpp
index 861e1994..9c31db5d 100644
--- a/lib/csapi/device_management.cpp
+++ b/lib/csapi/device_management.cpp
@@ -43,7 +43,7 @@ const QVector<Device>& GetDevicesJob::devices() const
 BaseJob::Status GetDevicesJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->devices = fromJson<QVector<Device>>(json.value("devices"_ls));
+    fromJson(json.value("devices"_ls), d->devices);
     return Success;
 }
 
@@ -77,7 +77,7 @@ const Device& GetDeviceJob::data() const
 
 BaseJob::Status GetDeviceJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<Device>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
diff --git a/lib/csapi/directory.cpp b/lib/csapi/directory.cpp
index 5353f3bc..4af86f7b 100644
--- a/lib/csapi/directory.cpp
+++ b/lib/csapi/directory.cpp
@@ -60,8 +60,8 @@ const QStringList& GetRoomIdByAliasJob::servers() const
 BaseJob::Status GetRoomIdByAliasJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->roomId = fromJson<QString>(json.value("room_id"_ls));
-    d->servers = fromJson<QStringList>(json.value("servers"_ls));
+    fromJson(json.value("room_id"_ls), d->roomId);
+    fromJson(json.value("servers"_ls), d->servers);
     return Success;
 }
 
diff --git a/lib/csapi/event_context.cpp b/lib/csapi/event_context.cpp
index 806c1613..bb1f5301 100644
--- a/lib/csapi/event_context.cpp
+++ b/lib/csapi/event_context.cpp
@@ -82,12 +82,12 @@ StateEvents&& GetEventContextJob::state()
 BaseJob::Status GetEventContextJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->begin = fromJson<QString>(json.value("start"_ls));
-    d->end = fromJson<QString>(json.value("end"_ls));
-    d->eventsBefore = fromJson<RoomEvents>(json.value("events_before"_ls));
-    d->event = fromJson<RoomEventPtr>(json.value("event"_ls));
-    d->eventsAfter = fromJson<RoomEvents>(json.value("events_after"_ls));
-    d->state = fromJson<StateEvents>(json.value("state"_ls));
+    fromJson(json.value("start"_ls), d->begin);
+    fromJson(json.value("end"_ls), d->end);
+    fromJson(json.value("events_before"_ls), d->eventsBefore);
+    fromJson(json.value("event"_ls), d->event);
+    fromJson(json.value("events_after"_ls), d->eventsAfter);
+    fromJson(json.value("state"_ls), d->state);
     return Success;
 }
 
diff --git a/lib/csapi/filter.cpp b/lib/csapi/filter.cpp
index 77dc9b92..982e60b5 100644
--- a/lib/csapi/filter.cpp
+++ b/lib/csapi/filter.cpp
@@ -41,7 +41,7 @@ BaseJob::Status DefineFilterJob::parseJson(const QJsonDocument& data)
     if (!json.contains("filter_id"_ls))
         return { JsonParseError,
             "The key 'filter_id' not found in the response" };
-    d->filterId = fromJson<QString>(json.value("filter_id"_ls));
+    fromJson(json.value("filter_id"_ls), d->filterId);
     return Success;
 }
 
@@ -75,7 +75,7 @@ const Filter& GetFilterJob::data() const
 
 BaseJob::Status GetFilterJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<Filter>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
diff --git a/lib/csapi/joining.cpp b/lib/csapi/joining.cpp
index 71781154..00d930fa 100644
--- a/lib/csapi/joining.cpp
+++ b/lib/csapi/joining.cpp
@@ -16,15 +16,16 @@ namespace QMatrixClient
 {
     // Converters
 
-    QJsonObject toJson(const JoinRoomByIdJob::ThirdPartySigned& pod)
+    template <> struct JsonObjectConverter<JoinRoomByIdJob::ThirdPartySigned>
     {
-        QJsonObject jo;
-        addParam<>(jo, QStringLiteral("sender"), pod.sender);
-        addParam<>(jo, QStringLiteral("mxid"), pod.mxid);
-        addParam<>(jo, QStringLiteral("token"), pod.token);
-        addParam<>(jo, QStringLiteral("signatures"), pod.signatures);
-        return jo;
-    }
+        static void dumpTo(QJsonObject& jo, const JoinRoomByIdJob::ThirdPartySigned& pod)
+        {
+            addParam<>(jo, QStringLiteral("sender"), pod.sender);
+            addParam<>(jo, QStringLiteral("mxid"), pod.mxid);
+            addParam<>(jo, QStringLiteral("token"), pod.token);
+            addParam<>(jo, QStringLiteral("signatures"), pod.signatures);
+        }
+    };
 } // namespace QMatrixClient
 
 class JoinRoomByIdJob::Private
@@ -58,7 +59,7 @@ BaseJob::Status JoinRoomByIdJob::parseJson(const QJsonDocument& data)
     if (!json.contains("room_id"_ls))
         return { JsonParseError,
             "The key 'room_id' not found in the response" };
-    d->roomId = fromJson<QString>(json.value("room_id"_ls));
+    fromJson(json.value("room_id"_ls), d->roomId);
     return Success;
 }
 
@@ -66,22 +67,24 @@ namespace QMatrixClient
 {
     // Converters
 
-    QJsonObject toJson(const JoinRoomJob::Signed& pod)
+    template <> struct JsonObjectConverter<JoinRoomJob::Signed>
     {
-        QJsonObject jo;
-        addParam<>(jo, QStringLiteral("sender"), pod.sender);
-        addParam<>(jo, QStringLiteral("mxid"), pod.mxid);
-        addParam<>(jo, QStringLiteral("token"), pod.token);
-        addParam<>(jo, QStringLiteral("signatures"), pod.signatures);
-        return jo;
-    }
-
-    QJsonObject toJson(const JoinRoomJob::ThirdPartySigned& pod)
+        static void dumpTo(QJsonObject& jo, const JoinRoomJob::Signed& pod)
+        {
+            addParam<>(jo, QStringLiteral("sender"), pod.sender);
+            addParam<>(jo, QStringLiteral("mxid"), pod.mxid);
+            addParam<>(jo, QStringLiteral("token"), pod.token);
+            addParam<>(jo, QStringLiteral("signatures"), pod.signatures);
+        }
+    };
+
+    template <> struct JsonObjectConverter<JoinRoomJob::ThirdPartySigned>
     {
-        QJsonObject jo;
-        addParam<>(jo, QStringLiteral("signed"), pod.signedData);
-        return jo;
-    }
+        static void dumpTo(QJsonObject& jo, const JoinRoomJob::ThirdPartySigned& pod)
+        {
+            addParam<>(jo, QStringLiteral("signed"), pod.signedData);
+        }
+    };
 } // namespace QMatrixClient
 
 class JoinRoomJob::Private
@@ -123,7 +126,7 @@ BaseJob::Status JoinRoomJob::parseJson(const QJsonDocument& data)
     if (!json.contains("room_id"_ls))
         return { JsonParseError,
             "The key 'room_id' not found in the response" };
-    d->roomId = fromJson<QString>(json.value("room_id"_ls));
+    fromJson(json.value("room_id"_ls), d->roomId);
     return Success;
 }
 
diff --git a/lib/csapi/keys.cpp b/lib/csapi/keys.cpp
index c7492411..6c16a8a3 100644
--- a/lib/csapi/keys.cpp
+++ b/lib/csapi/keys.cpp
@@ -44,7 +44,7 @@ BaseJob::Status UploadKeysJob::parseJson(const QJsonDocument& data)
     if (!json.contains("one_time_key_counts"_ls))
         return { JsonParseError,
             "The key 'one_time_key_counts' not found in the response" };
-    d->oneTimeKeyCounts = fromJson<QHash<QString, int>>(json.value("one_time_key_counts"_ls));
+    fromJson(json.value("one_time_key_counts"_ls), d->oneTimeKeyCounts);
     return Success;
 }
 
@@ -52,27 +52,20 @@ namespace QMatrixClient
 {
     // Converters
 
-    template <> struct FromJsonObject<QueryKeysJob::UnsignedDeviceInfo>
+    template <> struct JsonObjectConverter<QueryKeysJob::UnsignedDeviceInfo>
     {
-        QueryKeysJob::UnsignedDeviceInfo operator()(const QJsonObject& jo) const
+        static void fillFrom(const QJsonObject& jo, QueryKeysJob::UnsignedDeviceInfo& result)
         {
-            QueryKeysJob::UnsignedDeviceInfo result;
-            result.deviceDisplayName =
-                fromJson<QString>(jo.value("device_display_name"_ls));
-
-            return result;
+            fromJson(jo.value("device_display_name"_ls), result.deviceDisplayName);
         }
     };
 
-    template <> struct FromJsonObject<QueryKeysJob::DeviceInformation>
+    template <> struct JsonObjectConverter<QueryKeysJob::DeviceInformation>
     {
-        QueryKeysJob::DeviceInformation operator()(const QJsonObject& jo) const
+        static void fillFrom(const QJsonObject& jo, QueryKeysJob::DeviceInformation& result)
         {
-            QueryKeysJob::DeviceInformation result;
-            result.unsignedData =
-                fromJson<QueryKeysJob::UnsignedDeviceInfo>(jo.value("unsigned"_ls));
-
-            return result;
+            fillFromJson<DeviceKeys>(jo, result);
+                    fromJson(jo.value("unsigned"_ls), result.unsignedData);
         }
     };
 } // namespace QMatrixClient
@@ -113,8 +106,8 @@ const QHash<QString, QHash<QString, QueryKeysJob::DeviceInformation>>& QueryKeys
 BaseJob::Status QueryKeysJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->failures = fromJson<QHash<QString, QJsonObject>>(json.value("failures"_ls));
-    d->deviceKeys = fromJson<QHash<QString, QHash<QString, DeviceInformation>>>(json.value("device_keys"_ls));
+    fromJson(json.value("failures"_ls), d->failures);
+    fromJson(json.value("device_keys"_ls), d->deviceKeys);
     return Success;
 }
 
@@ -153,8 +146,8 @@ const QHash<QString, QHash<QString, QVariant>>& ClaimKeysJob::oneTimeKeys() cons
 BaseJob::Status ClaimKeysJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->failures = fromJson<QHash<QString, QJsonObject>>(json.value("failures"_ls));
-    d->oneTimeKeys = fromJson<QHash<QString, QHash<QString, QVariant>>>(json.value("one_time_keys"_ls));
+    fromJson(json.value("failures"_ls), d->failures);
+    fromJson(json.value("one_time_keys"_ls), d->oneTimeKeys);
     return Success;
 }
 
@@ -205,8 +198,8 @@ const QStringList& GetKeysChangesJob::left() const
 BaseJob::Status GetKeysChangesJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->changed = fromJson<QStringList>(json.value("changed"_ls));
-    d->left = fromJson<QStringList>(json.value("left"_ls));
+    fromJson(json.value("changed"_ls), d->changed);
+    fromJson(json.value("left"_ls), d->left);
     return Success;
 }
 
diff --git a/lib/csapi/list_joined_rooms.cpp b/lib/csapi/list_joined_rooms.cpp
index a745dba1..85a9cae4 100644
--- a/lib/csapi/list_joined_rooms.cpp
+++ b/lib/csapi/list_joined_rooms.cpp
@@ -46,7 +46,7 @@ BaseJob::Status GetJoinedRoomsJob::parseJson(const QJsonDocument& data)
     if (!json.contains("joined_rooms"_ls))
         return { JsonParseError,
             "The key 'joined_rooms' not found in the response" };
-    d->joinedRooms = fromJson<QStringList>(json.value("joined_rooms"_ls));
+    fromJson(json.value("joined_rooms"_ls), d->joinedRooms);
     return Success;
 }
 
diff --git a/lib/csapi/list_public_rooms.cpp b/lib/csapi/list_public_rooms.cpp
index 2fdb2005..2a0cb0ff 100644
--- a/lib/csapi/list_public_rooms.cpp
+++ b/lib/csapi/list_public_rooms.cpp
@@ -43,7 +43,7 @@ const QString& GetRoomVisibilityOnDirectoryJob::visibility() const
 BaseJob::Status GetRoomVisibilityOnDirectoryJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->visibility = fromJson<QString>(json.value("visibility"_ls));
+    fromJson(json.value("visibility"_ls), d->visibility);
     return Success;
 }
 
@@ -100,7 +100,7 @@ const PublicRoomsResponse& GetPublicRoomsJob::data() const
 
 BaseJob::Status GetPublicRoomsJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<PublicRoomsResponse>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
@@ -108,12 +108,13 @@ namespace QMatrixClient
 {
     // Converters
 
-    QJsonObject toJson(const QueryPublicRoomsJob::Filter& pod)
+    template <> struct JsonObjectConverter<QueryPublicRoomsJob::Filter>
     {
-        QJsonObject jo;
-        addParam<IfNotEmpty>(jo, QStringLiteral("generic_search_term"), pod.genericSearchTerm);
-        return jo;
-    }
+        static void dumpTo(QJsonObject& jo, const QueryPublicRoomsJob::Filter& pod)
+        {
+            addParam<IfNotEmpty>(jo, QStringLiteral("generic_search_term"), pod.genericSearchTerm);
+        }
+    };
 } // namespace QMatrixClient
 
 class QueryPublicRoomsJob::Private
@@ -155,7 +156,7 @@ const PublicRoomsResponse& QueryPublicRoomsJob::data() const
 
 BaseJob::Status QueryPublicRoomsJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<PublicRoomsResponse>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
diff --git a/lib/csapi/login.cpp b/lib/csapi/login.cpp
index 4d15a30b..ee33dac2 100644
--- a/lib/csapi/login.cpp
+++ b/lib/csapi/login.cpp
@@ -16,15 +16,11 @@ namespace QMatrixClient
 {
     // Converters
 
-    template <> struct FromJsonObject<GetLoginFlowsJob::LoginFlow>
+    template <> struct JsonObjectConverter<GetLoginFlowsJob::LoginFlow>
     {
-        GetLoginFlowsJob::LoginFlow operator()(const QJsonObject& jo) const
+        static void fillFrom(const QJsonObject& jo, GetLoginFlowsJob::LoginFlow& result)
         {
-            GetLoginFlowsJob::LoginFlow result;
-            result.type =
-                fromJson<QString>(jo.value("type"_ls));
-
-            return result;
+            fromJson(jo.value("type"_ls), result.type);
         }
     };
 } // namespace QMatrixClient
@@ -60,7 +56,7 @@ const QVector<GetLoginFlowsJob::LoginFlow>& GetLoginFlowsJob::flows() const
 BaseJob::Status GetLoginFlowsJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->flows = fromJson<QVector<LoginFlow>>(json.value("flows"_ls));
+    fromJson(json.value("flows"_ls), d->flows);
     return Success;
 }
 
@@ -118,10 +114,10 @@ const QString& LoginJob::deviceId() const
 BaseJob::Status LoginJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->userId = fromJson<QString>(json.value("user_id"_ls));
-    d->accessToken = fromJson<QString>(json.value("access_token"_ls));
-    d->homeServer = fromJson<QString>(json.value("home_server"_ls));
-    d->deviceId = fromJson<QString>(json.value("device_id"_ls));
+    fromJson(json.value("user_id"_ls), d->userId);
+    fromJson(json.value("access_token"_ls), d->accessToken);
+    fromJson(json.value("home_server"_ls), d->homeServer);
+    fromJson(json.value("device_id"_ls), d->deviceId);
     return Success;
 }
 
diff --git a/lib/csapi/message_pagination.cpp b/lib/csapi/message_pagination.cpp
index c59a51ab..9aca7ec9 100644
--- a/lib/csapi/message_pagination.cpp
+++ b/lib/csapi/message_pagination.cpp
@@ -68,9 +68,9 @@ RoomEvents&& GetRoomEventsJob::chunk()
 BaseJob::Status GetRoomEventsJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->begin = fromJson<QString>(json.value("start"_ls));
-    d->end = fromJson<QString>(json.value("end"_ls));
-    d->chunk = fromJson<RoomEvents>(json.value("chunk"_ls));
+    fromJson(json.value("start"_ls), d->begin);
+    fromJson(json.value("end"_ls), d->end);
+    fromJson(json.value("chunk"_ls), d->chunk);
     return Success;
 }
 
diff --git a/lib/csapi/notifications.cpp b/lib/csapi/notifications.cpp
index 785a0a8a..c00b7cb0 100644
--- a/lib/csapi/notifications.cpp
+++ b/lib/csapi/notifications.cpp
@@ -16,25 +16,16 @@ namespace QMatrixClient
 {
     // Converters
 
-    template <> struct FromJsonObject<GetNotificationsJob::Notification>
+    template <> struct JsonObjectConverter<GetNotificationsJob::Notification>
     {
-        GetNotificationsJob::Notification operator()(const QJsonObject& jo) const
+        static void fillFrom(const QJsonObject& jo, GetNotificationsJob::Notification& result)
         {
-            GetNotificationsJob::Notification result;
-            result.actions =
-                fromJson<QVector<QVariant>>(jo.value("actions"_ls));
-            result.event =
-                fromJson<EventPtr>(jo.value("event"_ls));
-            result.profileTag =
-                fromJson<QString>(jo.value("profile_tag"_ls));
-            result.read =
-                fromJson<bool>(jo.value("read"_ls));
-            result.roomId =
-                fromJson<QString>(jo.value("room_id"_ls));
-            result.ts =
-                fromJson<int>(jo.value("ts"_ls));
-
-            return result;
+            fromJson(jo.value("actions"_ls), result.actions);
+            fromJson(jo.value("event"_ls), result.event);
+            fromJson(jo.value("profile_tag"_ls), result.profileTag);
+            fromJson(jo.value("read"_ls), result.read);
+            fromJson(jo.value("room_id"_ls), result.roomId);
+            fromJson(jo.value("ts"_ls), result.ts);
         }
     };
 } // namespace QMatrixClient
@@ -87,11 +78,11 @@ std::vector<GetNotificationsJob::Notification>&& GetNotificationsJob::notificati
 BaseJob::Status GetNotificationsJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->nextToken = fromJson<QString>(json.value("next_token"_ls));
+    fromJson(json.value("next_token"_ls), d->nextToken);
     if (!json.contains("notifications"_ls))
         return { JsonParseError,
             "The key 'notifications' not found in the response" };
-    d->notifications = fromJson<std::vector<Notification>>(json.value("notifications"_ls));
+    fromJson(json.value("notifications"_ls), d->notifications);
     return Success;
 }
 
diff --git a/lib/csapi/openid.cpp b/lib/csapi/openid.cpp
index 2547f0c8..b27fe0b8 100644
--- a/lib/csapi/openid.cpp
+++ b/lib/csapi/openid.cpp
@@ -59,19 +59,19 @@ BaseJob::Status RequestOpenIdTokenJob::parseJson(const QJsonDocument& data)
     if (!json.contains("access_token"_ls))
         return { JsonParseError,
             "The key 'access_token' not found in the response" };
-    d->accessToken = fromJson<QString>(json.value("access_token"_ls));
+    fromJson(json.value("access_token"_ls), d->accessToken);
     if (!json.contains("token_type"_ls))
         return { JsonParseError,
             "The key 'token_type' not found in the response" };
-    d->tokenType = fromJson<QString>(json.value("token_type"_ls));
+    fromJson(json.value("token_type"_ls), d->tokenType);
     if (!json.contains("matrix_server_name"_ls))
         return { JsonParseError,
             "The key 'matrix_server_name' not found in the response" };
-    d->matrixServerName = fromJson<QString>(json.value("matrix_server_name"_ls));
+    fromJson(json.value("matrix_server_name"_ls), d->matrixServerName);
     if (!json.contains("expires_in"_ls))
         return { JsonParseError,
             "The key 'expires_in' not found in the response" };
-    d->expiresIn = fromJson<int>(json.value("expires_in"_ls));
+    fromJson(json.value("expires_in"_ls), d->expiresIn);
     return Success;
 }
 
diff --git a/lib/csapi/peeking_events.cpp b/lib/csapi/peeking_events.cpp
index e046a62e..3208d48d 100644
--- a/lib/csapi/peeking_events.cpp
+++ b/lib/csapi/peeking_events.cpp
@@ -66,9 +66,9 @@ RoomEvents&& PeekEventsJob::chunk()
 BaseJob::Status PeekEventsJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->begin = fromJson<QString>(json.value("start"_ls));
-    d->end = fromJson<QString>(json.value("end"_ls));
-    d->chunk = fromJson<RoomEvents>(json.value("chunk"_ls));
+    fromJson(json.value("start"_ls), d->begin);
+    fromJson(json.value("end"_ls), d->end);
+    fromJson(json.value("chunk"_ls), d->chunk);
     return Success;
 }
 
diff --git a/lib/csapi/presence.cpp b/lib/csapi/presence.cpp
index 7aba8b61..94a3e6c5 100644
--- a/lib/csapi/presence.cpp
+++ b/lib/csapi/presence.cpp
@@ -76,10 +76,10 @@ BaseJob::Status GetPresenceJob::parseJson(const QJsonDocument& data)
     if (!json.contains("presence"_ls))
         return { JsonParseError,
             "The key 'presence' not found in the response" };
-    d->presence = fromJson<QString>(json.value("presence"_ls));
-    d->lastActiveAgo = fromJson<int>(json.value("last_active_ago"_ls));
-    d->statusMsg = fromJson<QString>(json.value("status_msg"_ls));
-    d->currentlyActive = fromJson<bool>(json.value("currently_active"_ls));
+    fromJson(json.value("presence"_ls), d->presence);
+    fromJson(json.value("last_active_ago"_ls), d->lastActiveAgo);
+    fromJson(json.value("status_msg"_ls), d->statusMsg);
+    fromJson(json.value("currently_active"_ls), d->currentlyActive);
     return Success;
 }
 
@@ -125,7 +125,7 @@ Events&& GetPresenceForListJob::data()
 
 BaseJob::Status GetPresenceForListJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<Events>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
diff --git a/lib/csapi/profile.cpp b/lib/csapi/profile.cpp
index bb053062..4ed3ad9b 100644
--- a/lib/csapi/profile.cpp
+++ b/lib/csapi/profile.cpp
@@ -54,7 +54,7 @@ const QString& GetDisplayNameJob::displayname() const
 BaseJob::Status GetDisplayNameJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->displayname = fromJson<QString>(json.value("displayname"_ls));
+    fromJson(json.value("displayname"_ls), d->displayname);
     return Success;
 }
 
@@ -100,7 +100,7 @@ const QString& GetAvatarUrlJob::avatarUrl() const
 BaseJob::Status GetAvatarUrlJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->avatarUrl = fromJson<QString>(json.value("avatar_url"_ls));
+    fromJson(json.value("avatar_url"_ls), d->avatarUrl);
     return Success;
 }
 
@@ -141,8 +141,8 @@ const QString& GetUserProfileJob::displayname() const
 BaseJob::Status GetUserProfileJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->avatarUrl = fromJson<QString>(json.value("avatar_url"_ls));
-    d->displayname = fromJson<QString>(json.value("displayname"_ls));
+    fromJson(json.value("avatar_url"_ls), d->avatarUrl);
+    fromJson(json.value("displayname"_ls), d->displayname);
     return Success;
 }
 
diff --git a/lib/csapi/pusher.cpp b/lib/csapi/pusher.cpp
index d20db88a..3ad0dcbe 100644
--- a/lib/csapi/pusher.cpp
+++ b/lib/csapi/pusher.cpp
@@ -16,43 +16,27 @@ namespace QMatrixClient
 {
     // Converters
 
-    template <> struct FromJsonObject<GetPushersJob::PusherData>
+    template <> struct JsonObjectConverter<GetPushersJob::PusherData>
     {
-        GetPushersJob::PusherData operator()(const QJsonObject& jo) const
+        static void fillFrom(const QJsonObject& jo, GetPushersJob::PusherData& result)
         {
-            GetPushersJob::PusherData result;
-            result.url =
-                fromJson<QString>(jo.value("url"_ls));
-            result.format =
-                fromJson<QString>(jo.value("format"_ls));
-
-            return result;
+            fromJson(jo.value("url"_ls), result.url);
+            fromJson(jo.value("format"_ls), result.format);
         }
     };
 
-    template <> struct FromJsonObject<GetPushersJob::Pusher>
+    template <> struct JsonObjectConverter<GetPushersJob::Pusher>
     {
-        GetPushersJob::Pusher operator()(const QJsonObject& jo) const
+        static void fillFrom(const QJsonObject& jo, GetPushersJob::Pusher& result)
         {
-            GetPushersJob::Pusher result;
-            result.pushkey =
-                fromJson<QString>(jo.value("pushkey"_ls));
-            result.kind =
-                fromJson<QString>(jo.value("kind"_ls));
-            result.appId =
-                fromJson<QString>(jo.value("app_id"_ls));
-            result.appDisplayName =
-                fromJson<QString>(jo.value("app_display_name"_ls));
-            result.deviceDisplayName =
-                fromJson<QString>(jo.value("device_display_name"_ls));
-            result.profileTag =
-                fromJson<QString>(jo.value("profile_tag"_ls));
-            result.lang =
-                fromJson<QString>(jo.value("lang"_ls));
-            result.data =
-                fromJson<GetPushersJob::PusherData>(jo.value("data"_ls));
-
-            return result;
+            fromJson(jo.value("pushkey"_ls), result.pushkey);
+            fromJson(jo.value("kind"_ls), result.kind);
+            fromJson(jo.value("app_id"_ls), result.appId);
+            fromJson(jo.value("app_display_name"_ls), result.appDisplayName);
+            fromJson(jo.value("device_display_name"_ls), result.deviceDisplayName);
+            fromJson(jo.value("profile_tag"_ls), result.profileTag);
+            fromJson(jo.value("lang"_ls), result.lang);
+            fromJson(jo.value("data"_ls), result.data);
         }
     };
 } // namespace QMatrixClient
@@ -88,7 +72,7 @@ const QVector<GetPushersJob::Pusher>& GetPushersJob::pushers() const
 BaseJob::Status GetPushersJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->pushers = fromJson<QVector<Pusher>>(json.value("pushers"_ls));
+    fromJson(json.value("pushers"_ls), d->pushers);
     return Success;
 }
 
@@ -96,13 +80,14 @@ namespace QMatrixClient
 {
     // Converters
 
-    QJsonObject toJson(const PostPusherJob::PusherData& pod)
+    template <> struct JsonObjectConverter<PostPusherJob::PusherData>
     {
-        QJsonObject jo;
-        addParam<IfNotEmpty>(jo, QStringLiteral("url"), pod.url);
-        addParam<IfNotEmpty>(jo, QStringLiteral("format"), pod.format);
-        return jo;
-    }
+        static void dumpTo(QJsonObject& jo, const PostPusherJob::PusherData& pod)
+        {
+            addParam<IfNotEmpty>(jo, QStringLiteral("url"), pod.url);
+            addParam<IfNotEmpty>(jo, QStringLiteral("format"), pod.format);
+        }
+    };
 } // namespace QMatrixClient
 
 static const auto PostPusherJobName = QStringLiteral("PostPusherJob");
diff --git a/lib/csapi/pushrules.cpp b/lib/csapi/pushrules.cpp
index ea8ad02a..b91d18f7 100644
--- a/lib/csapi/pushrules.cpp
+++ b/lib/csapi/pushrules.cpp
@@ -46,7 +46,7 @@ BaseJob::Status GetPushRulesJob::parseJson(const QJsonDocument& data)
     if (!json.contains("global"_ls))
         return { JsonParseError,
             "The key 'global' not found in the response" };
-    d->global = fromJson<PushRuleset>(json.value("global"_ls));
+    fromJson(json.value("global"_ls), d->global);
     return Success;
 }
 
@@ -80,7 +80,7 @@ const PushRule& GetPushRuleJob::data() const
 
 BaseJob::Status GetPushRuleJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<PushRule>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
@@ -154,7 +154,7 @@ BaseJob::Status IsPushRuleEnabledJob::parseJson(const QJsonDocument& data)
     if (!json.contains("enabled"_ls))
         return { JsonParseError,
             "The key 'enabled' not found in the response" };
-    d->enabled = fromJson<bool>(json.value("enabled"_ls));
+    fromJson(json.value("enabled"_ls), d->enabled);
     return Success;
 }
 
@@ -203,7 +203,7 @@ BaseJob::Status GetPushRuleActionsJob::parseJson(const QJsonDocument& data)
     if (!json.contains("actions"_ls))
         return { JsonParseError,
             "The key 'actions' not found in the response" };
-    d->actions = fromJson<QStringList>(json.value("actions"_ls));
+    fromJson(json.value("actions"_ls), d->actions);
     return Success;
 }
 
diff --git a/lib/csapi/redaction.cpp b/lib/csapi/redaction.cpp
index 64098670..1d54e36d 100644
--- a/lib/csapi/redaction.cpp
+++ b/lib/csapi/redaction.cpp
@@ -40,7 +40,7 @@ const QString& RedactEventJob::eventId() const
 BaseJob::Status RedactEventJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->eventId = fromJson<QString>(json.value("event_id"_ls));
+    fromJson(json.value("event_id"_ls), d->eventId);
     return Success;
 }
 
diff --git a/lib/csapi/registration.cpp b/lib/csapi/registration.cpp
index 320ec796..2772cd57 100644
--- a/lib/csapi/registration.cpp
+++ b/lib/csapi/registration.cpp
@@ -76,10 +76,10 @@ BaseJob::Status RegisterJob::parseJson(const QJsonDocument& data)
     if (!json.contains("user_id"_ls))
         return { JsonParseError,
             "The key 'user_id' not found in the response" };
-    d->userId = fromJson<QString>(json.value("user_id"_ls));
-    d->accessToken = fromJson<QString>(json.value("access_token"_ls));
-    d->homeServer = fromJson<QString>(json.value("home_server"_ls));
-    d->deviceId = fromJson<QString>(json.value("device_id"_ls));
+    fromJson(json.value("user_id"_ls), d->userId);
+    fromJson(json.value("access_token"_ls), d->accessToken);
+    fromJson(json.value("home_server"_ls), d->homeServer);
+    fromJson(json.value("device_id"_ls), d->deviceId);
     return Success;
 }
 
@@ -114,7 +114,7 @@ const Sid& RequestTokenToRegisterEmailJob::data() const
 
 BaseJob::Status RequestTokenToRegisterEmailJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<Sid>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
@@ -150,7 +150,7 @@ const Sid& RequestTokenToRegisterMSISDNJob::data() const
 
 BaseJob::Status RequestTokenToRegisterMSISDNJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<Sid>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
@@ -197,7 +197,7 @@ const Sid& RequestTokenToResetPasswordEmailJob::data() const
 
 BaseJob::Status RequestTokenToResetPasswordEmailJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<Sid>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
@@ -233,7 +233,7 @@ const Sid& RequestTokenToResetPasswordMSISDNJob::data() const
 
 BaseJob::Status RequestTokenToResetPasswordMSISDNJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<Sid>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
@@ -289,7 +289,7 @@ bool CheckUsernameAvailabilityJob::available() const
 BaseJob::Status CheckUsernameAvailabilityJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->available = fromJson<bool>(json.value("available"_ls));
+    fromJson(json.value("available"_ls), d->available);
     return Success;
 }
 
diff --git a/lib/csapi/room_send.cpp b/lib/csapi/room_send.cpp
index 2b39ede2..0d25eb69 100644
--- a/lib/csapi/room_send.cpp
+++ b/lib/csapi/room_send.cpp
@@ -38,7 +38,7 @@ const QString& SendMessageJob::eventId() const
 BaseJob::Status SendMessageJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->eventId = fromJson<QString>(json.value("event_id"_ls));
+    fromJson(json.value("event_id"_ls), d->eventId);
     return Success;
 }
 
diff --git a/lib/csapi/room_state.cpp b/lib/csapi/room_state.cpp
index 8f87979d..3aa7d736 100644
--- a/lib/csapi/room_state.cpp
+++ b/lib/csapi/room_state.cpp
@@ -38,7 +38,7 @@ const QString& SetRoomStateWithKeyJob::eventId() const
 BaseJob::Status SetRoomStateWithKeyJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->eventId = fromJson<QString>(json.value("event_id"_ls));
+    fromJson(json.value("event_id"_ls), d->eventId);
     return Success;
 }
 
@@ -68,7 +68,7 @@ const QString& SetRoomStateJob::eventId() const
 BaseJob::Status SetRoomStateJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->eventId = fromJson<QString>(json.value("event_id"_ls));
+    fromJson(json.value("event_id"_ls), d->eventId);
     return Success;
 }
 
diff --git a/lib/csapi/rooms.cpp b/lib/csapi/rooms.cpp
index cebb295a..0b08ccec 100644
--- a/lib/csapi/rooms.cpp
+++ b/lib/csapi/rooms.cpp
@@ -42,7 +42,7 @@ EventPtr&& GetOneRoomEventJob::data()
 
 BaseJob::Status GetOneRoomEventJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<EventPtr>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
@@ -104,7 +104,7 @@ StateEvents&& GetRoomStateJob::data()
 
 BaseJob::Status GetRoomStateJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<StateEvents>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
@@ -114,17 +114,28 @@ class GetMembersByRoomJob::Private
         EventsArray<RoomMemberEvent> chunk;
 };
 
-QUrl GetMembersByRoomJob::makeRequestUrl(QUrl baseUrl, const QString& roomId)
+BaseJob::Query queryToGetMembersByRoom(const QString& at, const QString& membership, const QString& notMembership)
+{
+    BaseJob::Query _q;
+    addParam<IfNotEmpty>(_q, QStringLiteral("at"), at);
+    addParam<IfNotEmpty>(_q, QStringLiteral("membership"), membership);
+    addParam<IfNotEmpty>(_q, QStringLiteral("not_membership"), notMembership);
+    return _q;
+}
+
+QUrl GetMembersByRoomJob::makeRequestUrl(QUrl baseUrl, const QString& roomId, const QString& at, const QString& membership, const QString& notMembership)
 {
     return BaseJob::makeRequestUrl(std::move(baseUrl),
-            basePath % "/rooms/" % roomId % "/members");
+            basePath % "/rooms/" % roomId % "/members",
+            queryToGetMembersByRoom(at, membership, notMembership));
 }
 
 static const auto GetMembersByRoomJobName = QStringLiteral("GetMembersByRoomJob");
 
-GetMembersByRoomJob::GetMembersByRoomJob(const QString& roomId)
+GetMembersByRoomJob::GetMembersByRoomJob(const QString& roomId, const QString& at, const QString& membership, const QString& notMembership)
     : BaseJob(HttpVerb::Get, GetMembersByRoomJobName,
-        basePath % "/rooms/" % roomId % "/members")
+        basePath % "/rooms/" % roomId % "/members",
+        queryToGetMembersByRoom(at, membership, notMembership))
     , d(new Private)
 {
 }
@@ -139,7 +150,7 @@ EventsArray<RoomMemberEvent>&& GetMembersByRoomJob::chunk()
 BaseJob::Status GetMembersByRoomJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->chunk = fromJson<EventsArray<RoomMemberEvent>>(json.value("chunk"_ls));
+    fromJson(json.value("chunk"_ls), d->chunk);
     return Success;
 }
 
@@ -147,17 +158,12 @@ namespace QMatrixClient
 {
     // Converters
 
-    template <> struct FromJsonObject<GetJoinedMembersByRoomJob::RoomMember>
+    template <> struct JsonObjectConverter<GetJoinedMembersByRoomJob::RoomMember>
     {
-        GetJoinedMembersByRoomJob::RoomMember operator()(const QJsonObject& jo) const
+        static void fillFrom(const QJsonObject& jo, GetJoinedMembersByRoomJob::RoomMember& result)
         {
-            GetJoinedMembersByRoomJob::RoomMember result;
-            result.displayName =
-                fromJson<QString>(jo.value("display_name"_ls));
-            result.avatarUrl =
-                fromJson<QString>(jo.value("avatar_url"_ls));
-
-            return result;
+            fromJson(jo.value("display_name"_ls), result.displayName);
+            fromJson(jo.value("avatar_url"_ls), result.avatarUrl);
         }
     };
 } // namespace QMatrixClient
@@ -193,7 +199,7 @@ const QHash<QString, GetJoinedMembersByRoomJob::RoomMember>& GetJoinedMembersByR
 BaseJob::Status GetJoinedMembersByRoomJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->joined = fromJson<QHash<QString, RoomMember>>(json.value("joined"_ls));
+    fromJson(json.value("joined"_ls), d->joined);
     return Success;
 }
 
diff --git a/lib/csapi/rooms.h b/lib/csapi/rooms.h
index 80895b4e..415aa4ed 100644
--- a/lib/csapi/rooms.h
+++ b/lib/csapi/rooms.h
@@ -158,8 +158,17 @@ namespace QMatrixClient
             /*! Get the m.room.member events for the room.
              * \param roomId
              *   The room to get the member events for.
+             * \param at
+             *   The token defining the timeline position as-of which to return
+             *   the list of members. This token can be obtained from
+             *   a ``prev_batch`` token returned for each room by the sync API, or
+             *   from a ``start`` or ``end`` token returned by a /messages request.
+             * \param membership
+             *   Only return users with the specified membership
+             * \param notMembership
+             *   Only return users with membership state other than specified
              */
-            explicit GetMembersByRoomJob(const QString& roomId);
+            explicit GetMembersByRoomJob(const QString& roomId, const QString& at = {}, const QString& membership = {}, const QString& notMembership = {});
 
             /*! Construct a URL without creating a full-fledged job object
              *
@@ -167,7 +176,7 @@ namespace QMatrixClient
              * GetMembersByRoomJob is necessary but the job
              * itself isn't.
              */
-            static QUrl makeRequestUrl(QUrl baseUrl, const QString& roomId);
+            static QUrl makeRequestUrl(QUrl baseUrl, const QString& roomId, const QString& at = {}, const QString& membership = {}, const QString& notMembership = {});
 
             ~GetMembersByRoomJob() override;
 
diff --git a/lib/csapi/search.cpp b/lib/csapi/search.cpp
index 9436eb47..a5f83c79 100644
--- a/lib/csapi/search.cpp
+++ b/lib/csapi/search.cpp
@@ -16,146 +16,113 @@ namespace QMatrixClient
 {
     // Converters
 
-    QJsonObject toJson(const SearchJob::IncludeEventContext& pod)
+    template <> struct JsonObjectConverter<SearchJob::IncludeEventContext>
     {
-        QJsonObject jo;
-        addParam<IfNotEmpty>(jo, QStringLiteral("before_limit"), pod.beforeLimit);
-        addParam<IfNotEmpty>(jo, QStringLiteral("after_limit"), pod.afterLimit);
-        addParam<IfNotEmpty>(jo, QStringLiteral("include_profile"), pod.includeProfile);
-        return jo;
-    }
-
-    QJsonObject toJson(const SearchJob::Group& pod)
-    {
-        QJsonObject jo;
-        addParam<IfNotEmpty>(jo, QStringLiteral("key"), pod.key);
-        return jo;
-    }
+        static void dumpTo(QJsonObject& jo, const SearchJob::IncludeEventContext& pod)
+        {
+            addParam<IfNotEmpty>(jo, QStringLiteral("before_limit"), pod.beforeLimit);
+            addParam<IfNotEmpty>(jo, QStringLiteral("after_limit"), pod.afterLimit);
+            addParam<IfNotEmpty>(jo, QStringLiteral("include_profile"), pod.includeProfile);
+        }
+    };
 
-    QJsonObject toJson(const SearchJob::Groupings& pod)
+    template <> struct JsonObjectConverter<SearchJob::Group>
     {
-        QJsonObject jo;
-        addParam<IfNotEmpty>(jo, QStringLiteral("group_by"), pod.groupBy);
-        return jo;
-    }
+        static void dumpTo(QJsonObject& jo, const SearchJob::Group& pod)
+        {
+            addParam<IfNotEmpty>(jo, QStringLiteral("key"), pod.key);
+        }
+    };
 
-    QJsonObject toJson(const SearchJob::RoomEventsCriteria& pod)
-    {
-        QJsonObject jo;
-        addParam<>(jo, QStringLiteral("search_term"), pod.searchTerm);
-        addParam<IfNotEmpty>(jo, QStringLiteral("keys"), pod.keys);
-        addParam<IfNotEmpty>(jo, QStringLiteral("filter"), pod.filter);
-        addParam<IfNotEmpty>(jo, QStringLiteral("order_by"), pod.orderBy);
-        addParam<IfNotEmpty>(jo, QStringLiteral("event_context"), pod.eventContext);
-        addParam<IfNotEmpty>(jo, QStringLiteral("include_state"), pod.includeState);
-        addParam<IfNotEmpty>(jo, QStringLiteral("groupings"), pod.groupings);
-        return jo;
-    }
-
-    QJsonObject toJson(const SearchJob::Categories& pod)
+    template <> struct JsonObjectConverter<SearchJob::Groupings>
     {
-        QJsonObject jo;
-        addParam<IfNotEmpty>(jo, QStringLiteral("room_events"), pod.roomEvents);
-        return jo;
-    }
+        static void dumpTo(QJsonObject& jo, const SearchJob::Groupings& pod)
+        {
+            addParam<IfNotEmpty>(jo, QStringLiteral("group_by"), pod.groupBy);
+        }
+    };
 
-    template <> struct FromJsonObject<SearchJob::UserProfile>
+    template <> struct JsonObjectConverter<SearchJob::RoomEventsCriteria>
     {
-        SearchJob::UserProfile operator()(const QJsonObject& jo) const
+        static void dumpTo(QJsonObject& jo, const SearchJob::RoomEventsCriteria& pod)
         {
-            SearchJob::UserProfile result;
-            result.displayname =
-                fromJson<QString>(jo.value("displayname"_ls));
-            result.avatarUrl =
-                fromJson<QString>(jo.value("avatar_url"_ls));
+            addParam<>(jo, QStringLiteral("search_term"), pod.searchTerm);
+            addParam<IfNotEmpty>(jo, QStringLiteral("keys"), pod.keys);
+            addParam<IfNotEmpty>(jo, QStringLiteral("filter"), pod.filter);
+            addParam<IfNotEmpty>(jo, QStringLiteral("order_by"), pod.orderBy);
+            addParam<IfNotEmpty>(jo, QStringLiteral("event_context"), pod.eventContext);
+            addParam<IfNotEmpty>(jo, QStringLiteral("include_state"), pod.includeState);
+            addParam<IfNotEmpty>(jo, QStringLiteral("groupings"), pod.groupings);
+        }
+    };
 
-            return result;
+    template <> struct JsonObjectConverter<SearchJob::Categories>
+    {
+        static void dumpTo(QJsonObject& jo, const SearchJob::Categories& pod)
+        {
+            addParam<IfNotEmpty>(jo, QStringLiteral("room_events"), pod.roomEvents);
         }
     };
 
-    template <> struct FromJsonObject<SearchJob::EventContext>
+    template <> struct JsonObjectConverter<SearchJob::UserProfile>
     {
-        SearchJob::EventContext operator()(const QJsonObject& jo) const
+        static void fillFrom(const QJsonObject& jo, SearchJob::UserProfile& result)
         {
-            SearchJob::EventContext result;
-            result.begin =
-                fromJson<QString>(jo.value("start"_ls));
-            result.end =
-                fromJson<QString>(jo.value("end"_ls));
-            result.profileInfo =
-                fromJson<QHash<QString, SearchJob::UserProfile>>(jo.value("profile_info"_ls));
-            result.eventsBefore =
-                fromJson<RoomEvents>(jo.value("events_before"_ls));
-            result.eventsAfter =
-                fromJson<RoomEvents>(jo.value("events_after"_ls));
-
-            return result;
+            fromJson(jo.value("displayname"_ls), result.displayname);
+            fromJson(jo.value("avatar_url"_ls), result.avatarUrl);
         }
     };
 
-    template <> struct FromJsonObject<SearchJob::Result>
+    template <> struct JsonObjectConverter<SearchJob::EventContext>
     {
-        SearchJob::Result operator()(const QJsonObject& jo) const
+        static void fillFrom(const QJsonObject& jo, SearchJob::EventContext& result)
         {
-            SearchJob::Result result;
-            result.rank =
-                fromJson<double>(jo.value("rank"_ls));
-            result.result =
-                fromJson<RoomEventPtr>(jo.value("result"_ls));
-            result.context =
-                fromJson<SearchJob::EventContext>(jo.value("context"_ls));
-
-            return result;
+            fromJson(jo.value("start"_ls), result.begin);
+            fromJson(jo.value("end"_ls), result.end);
+            fromJson(jo.value("profile_info"_ls), result.profileInfo);
+            fromJson(jo.value("events_before"_ls), result.eventsBefore);
+            fromJson(jo.value("events_after"_ls), result.eventsAfter);
         }
     };
 
-    template <> struct FromJsonObject<SearchJob::GroupValue>
+    template <> struct JsonObjectConverter<SearchJob::Result>
     {
-        SearchJob::GroupValue operator()(const QJsonObject& jo) const
+        static void fillFrom(const QJsonObject& jo, SearchJob::Result& result)
         {
-            SearchJob::GroupValue result;
-            result.nextBatch =
-                fromJson<QString>(jo.value("next_batch"_ls));
-            result.order =
-                fromJson<int>(jo.value("order"_ls));
-            result.results =
-                fromJson<QStringList>(jo.value("results"_ls));
-
-            return result;
+            fromJson(jo.value("rank"_ls), result.rank);
+            fromJson(jo.value("result"_ls), result.result);
+            fromJson(jo.value("context"_ls), result.context);
         }
     };
 
-    template <> struct FromJsonObject<SearchJob::ResultRoomEvents>
+    template <> struct JsonObjectConverter<SearchJob::GroupValue>
     {
-        SearchJob::ResultRoomEvents operator()(const QJsonObject& jo) const
+        static void fillFrom(const QJsonObject& jo, SearchJob::GroupValue& result)
         {
-            SearchJob::ResultRoomEvents result;
-            result.count =
-                fromJson<int>(jo.value("count"_ls));
-            result.highlights =
-                fromJson<QStringList>(jo.value("highlights"_ls));
-            result.results =
-                fromJson<std::vector<SearchJob::Result>>(jo.value("results"_ls));
-            result.state =
-                fromJson<std::unordered_map<QString, StateEvents>>(jo.value("state"_ls));
-            result.groups =
-                fromJson<QHash<QString, QHash<QString, SearchJob::GroupValue>>>(jo.value("groups"_ls));
-            result.nextBatch =
-                fromJson<QString>(jo.value("next_batch"_ls));
-
-            return result;
+            fromJson(jo.value("next_batch"_ls), result.nextBatch);
+            fromJson(jo.value("order"_ls), result.order);
+            fromJson(jo.value("results"_ls), result.results);
         }
     };
 
-    template <> struct FromJsonObject<SearchJob::ResultCategories>
+    template <> struct JsonObjectConverter<SearchJob::ResultRoomEvents>
     {
-        SearchJob::ResultCategories operator()(const QJsonObject& jo) const
+        static void fillFrom(const QJsonObject& jo, SearchJob::ResultRoomEvents& result)
         {
-            SearchJob::ResultCategories result;
-            result.roomEvents =
-                fromJson<SearchJob::ResultRoomEvents>(jo.value("room_events"_ls));
+            fromJson(jo.value("count"_ls), result.count);
+            fromJson(jo.value("highlights"_ls), result.highlights);
+            fromJson(jo.value("results"_ls), result.results);
+            fromJson(jo.value("state"_ls), result.state);
+            fromJson(jo.value("groups"_ls), result.groups);
+            fromJson(jo.value("next_batch"_ls), result.nextBatch);
+        }
+    };
 
-            return result;
+    template <> struct JsonObjectConverter<SearchJob::ResultCategories>
+    {
+        static void fillFrom(const QJsonObject& jo, SearchJob::ResultCategories& result)
+        {
+            fromJson(jo.value("room_events"_ls), result.roomEvents);
         }
     };
 } // namespace QMatrixClient
@@ -199,7 +166,7 @@ BaseJob::Status SearchJob::parseJson(const QJsonDocument& data)
     if (!json.contains("search_categories"_ls))
         return { JsonParseError,
             "The key 'search_categories' not found in the response" };
-    d->searchCategories = fromJson<ResultCategories>(json.value("search_categories"_ls));
+    fromJson(json.value("search_categories"_ls), d->searchCategories);
     return Success;
 }
 
diff --git a/lib/csapi/tags.cpp b/lib/csapi/tags.cpp
index 808915ac..94026bb9 100644
--- a/lib/csapi/tags.cpp
+++ b/lib/csapi/tags.cpp
@@ -16,16 +16,12 @@ namespace QMatrixClient
 {
     // Converters
 
-    template <> struct FromJsonObject<GetRoomTagsJob::Tag>
+    template <> struct JsonObjectConverter<GetRoomTagsJob::Tag>
     {
-        GetRoomTagsJob::Tag operator()(QJsonObject jo) const
+        static void fillFrom(QJsonObject jo, GetRoomTagsJob::Tag& result)
         {
-            GetRoomTagsJob::Tag result;
-            result.order =
-                fromJson<float>(jo.take("order"_ls));
-
-            result.additionalProperties = fromJson<QVariantHash>(jo);
-            return result;
+            fromJson(jo.take("order"_ls), result.order);
+            fromJson(jo, result.additionalProperties);
         }
     };
 } // namespace QMatrixClient
@@ -61,7 +57,7 @@ const QHash<QString, GetRoomTagsJob::Tag>& GetRoomTagsJob::tags() const
 BaseJob::Status GetRoomTagsJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->tags = fromJson<QHash<QString, Tag>>(json.value("tags"_ls));
+    fromJson(json.value("tags"_ls), d->tags);
     return Success;
 }
 
diff --git a/lib/csapi/third_party_lookup.cpp b/lib/csapi/third_party_lookup.cpp
index 3ba1a5ad..12cb7c59 100644
--- a/lib/csapi/third_party_lookup.cpp
+++ b/lib/csapi/third_party_lookup.cpp
@@ -42,7 +42,7 @@ const QHash<QString, ThirdPartyProtocol>& GetProtocolsJob::data() const
 
 BaseJob::Status GetProtocolsJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<QHash<QString, ThirdPartyProtocol>>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
@@ -76,7 +76,7 @@ const ThirdPartyProtocol& GetProtocolMetadataJob::data() const
 
 BaseJob::Status GetProtocolMetadataJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<ThirdPartyProtocol>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
@@ -119,7 +119,7 @@ const QVector<ThirdPartyLocation>& QueryLocationByProtocolJob::data() const
 
 BaseJob::Status QueryLocationByProtocolJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<QVector<ThirdPartyLocation>>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
@@ -162,7 +162,7 @@ const QVector<ThirdPartyUser>& QueryUserByProtocolJob::data() const
 
 BaseJob::Status QueryUserByProtocolJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<QVector<ThirdPartyUser>>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
@@ -205,7 +205,7 @@ const QVector<ThirdPartyLocation>& QueryLocationByAliasJob::data() const
 
 BaseJob::Status QueryLocationByAliasJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<QVector<ThirdPartyLocation>>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
@@ -248,7 +248,7 @@ const QVector<ThirdPartyUser>& QueryUserByIDJob::data() const
 
 BaseJob::Status QueryUserByIDJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<QVector<ThirdPartyUser>>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
diff --git a/lib/csapi/users.cpp b/lib/csapi/users.cpp
index deb9cb8a..97d8962d 100644
--- a/lib/csapi/users.cpp
+++ b/lib/csapi/users.cpp
@@ -16,19 +16,13 @@ namespace QMatrixClient
 {
     // Converters
 
-    template <> struct FromJsonObject<SearchUserDirectoryJob::User>
+    template <> struct JsonObjectConverter<SearchUserDirectoryJob::User>
     {
-        SearchUserDirectoryJob::User operator()(const QJsonObject& jo) const
+        static void fillFrom(const QJsonObject& jo, SearchUserDirectoryJob::User& result)
         {
-            SearchUserDirectoryJob::User result;
-            result.userId =
-                fromJson<QString>(jo.value("user_id"_ls));
-            result.displayName =
-                fromJson<QString>(jo.value("display_name"_ls));
-            result.avatarUrl =
-                fromJson<QString>(jo.value("avatar_url"_ls));
-
-            return result;
+            fromJson(jo.value("user_id"_ls), result.userId);
+            fromJson(jo.value("display_name"_ls), result.displayName);
+            fromJson(jo.value("avatar_url"_ls), result.avatarUrl);
         }
     };
 } // namespace QMatrixClient
@@ -71,11 +65,11 @@ BaseJob::Status SearchUserDirectoryJob::parseJson(const QJsonDocument& data)
     if (!json.contains("results"_ls))
         return { JsonParseError,
             "The key 'results' not found in the response" };
-    d->results = fromJson<QVector<User>>(json.value("results"_ls));
+    fromJson(json.value("results"_ls), d->results);
     if (!json.contains("limited"_ls))
         return { JsonParseError,
             "The key 'limited' not found in the response" };
-    d->limited = fromJson<bool>(json.value("limited"_ls));
+    fromJson(json.value("limited"_ls), d->limited);
     return Success;
 }
 
diff --git a/lib/csapi/versions.cpp b/lib/csapi/versions.cpp
index 128902e2..c853ec06 100644
--- a/lib/csapi/versions.cpp
+++ b/lib/csapi/versions.cpp
@@ -43,7 +43,7 @@ const QStringList& GetVersionsJob::versions() const
 BaseJob::Status GetVersionsJob::parseJson(const QJsonDocument& data)
 {
     auto json = data.object();
-    d->versions = fromJson<QStringList>(json.value("versions"_ls));
+    fromJson(json.value("versions"_ls), d->versions);
     return Success;
 }
 
diff --git a/lib/csapi/voip.cpp b/lib/csapi/voip.cpp
index 0479b645..e8158723 100644
--- a/lib/csapi/voip.cpp
+++ b/lib/csapi/voip.cpp
@@ -42,7 +42,7 @@ const QJsonObject& GetTurnServerJob::data() const
 
 BaseJob::Status GetTurnServerJob::parseJson(const QJsonDocument& data)
 {
-    d->data = fromJson<QJsonObject>(data);
+    fromJson(data, d->data);
     return Success;
 }
 
diff --git a/lib/csapi/wellknown.cpp b/lib/csapi/wellknown.cpp
index d42534a0..97505830 100644
--- a/lib/csapi/wellknown.cpp
+++ b/lib/csapi/wellknown.cpp
@@ -52,8 +52,8 @@ BaseJob::Status GetWellknownJob::parseJson(const QJsonDocument& data)
     if (!json.contains("m.homeserver"_ls))
         return { JsonParseError,
             "The key 'm.homeserver' not found in the response" };
-    d->homeserver = fromJson<HomeserverInformation>(json.value("m.homeserver"_ls));
-    d->identityServer = fromJson<IdentityServerInformation>(json.value("m.identity_server"_ls));
+    fromJson(json.value("m.homeserver"_ls), d->homeserver);
+    fromJson(json.value("m.identity_server"_ls), d->identityServer);
     return Success;
 }
 
diff --git a/lib/csapi/whoami.cpp b/lib/csapi/whoami.cpp
index cb6439ef..aebdf5d3 100644
--- a/lib/csapi/whoami.cpp
+++ b/lib/csapi/whoami.cpp
@@ -46,7 +46,7 @@ BaseJob::Status GetTokenOwnerJob::parseJson(const QJsonDocument& data)
     if (!json.contains("user_id"_ls))
         return { JsonParseError,
             "The key 'user_id' not found in the response" };
-    d->userId = fromJson<QString>(json.value("user_id"_ls));
+    fromJson(json.value("user_id"_ls), d->userId);
     return Success;
 }
 
diff --git a/lib/csapi/{{base}}.cpp.mustache b/lib/csapi/{{base}}.cpp.mustache
index 64fd8bf3..ff888d76 100644
--- a/lib/csapi/{{base}}.cpp.mustache
+++ b/lib/csapi/{{base}}.cpp.mustache
@@ -8,49 +8,52 @@
 {{/operations}}
 using namespace QMatrixClient;
 {{#models.model}}{{#in?}}
-QJsonObject QMatrixClient::toJson(const {{qualifiedName}}& pod)
+void JsonObjectConverter<{{qualifiedName}}>::dumpTo(
+        QJsonObject& jo, const {{qualifiedName}}& pod)
 {
-    QJsonObject jo{{#propertyMap}} = toJson(pod.{{nameCamelCase}}){{/propertyMap}};{{#vars}}
-    addParam<{{^required?}}IfNotEmpty{{/required?}}>(jo, QStringLiteral("{{baseName}}"), pod.{{nameCamelCase}});{{/vars}}
-    return jo;
-}
+{{#propertyMap}}    fillJson(jo, pod.{{nameCamelCase}});
+{{/propertyMap}}{{#parents}}    fillJson<{{name}}>(jo, pod);
+{{/parents}}{{#vars}}    addParam<{{^required?}}IfNotEmpty{{/required?}}>(jo, QStringLiteral("{{baseName}}"), pod.{{nameCamelCase}});
+{{/vars}}}{{!<- dumpTo() ends here}}
 {{/in?}}{{#out?}}
-{{qualifiedName}} FromJsonObject<{{qualifiedName}}>::operator()({{^propertyMap}}const QJsonObject&{{/propertyMap}}{{#propertyMap}}QJsonObject{{/propertyMap}} jo) const
+void JsonObjectConverter<{{qualifiedName}}>::fillFrom(
+    {{^propertyMap}}const QJsonObject&{{/propertyMap
+  }}{{#propertyMap}}QJsonObject{{/propertyMap}} jo, {{qualifiedName}}& result)
 {
-    {{qualifiedName}} result;
-{{#vars}}    result.{{nameCamelCase}} =
-        fromJson<{{dataType.qualifiedName}}>(jo.{{#propertyMap}}take{{/propertyMap}}{{^propertyMap}}value{{/propertyMap}}("{{baseName}}"_ls));
+{{#parents}}    fillFromJson<{{qualifiedName}}>(jo, result);
+{{/parents}}{{#vars}}    fromJson(jo.{{#propertyMap}}take{{/propertyMap
+                                   }}{{^propertyMap}}value{{/propertyMap}}("{{baseName}}"_ls), result.{{nameCamelCase}});
 {{/vars}}{{#propertyMap}}
-    result.{{nameCamelCase}} = fromJson<{{dataType.qualifiedName}}>(jo);{{/propertyMap}}
-    return result;
-}
+    fromJson(jo, result.{{nameCamelCase}});
+{{/propertyMap}}}
 {{/out?}}{{/models.model}}{{#operations}}
 static const auto basePath = QStringLiteral("{{basePathWithoutHost}}");
 {{#    operation}}{{#models}}
 namespace QMatrixClient
 {
     // Converters
-{{#model}}{{#in?}}
-    QJsonObject toJson(const {{qualifiedName}}& pod)
-    {
-        QJsonObject jo{{#propertyMap}} = toJson(pod.{{nameCamelCase}}){{/propertyMap}};{{#vars}}
-        addParam<{{^required?}}IfNotEmpty{{/required?}}>(jo, QStringLiteral("{{baseName}}"), pod.{{nameCamelCase}});{{/vars}}
-        return jo;
-    }
-{{/in?}}{{#out?}}
-    template <> struct FromJsonObject<{{qualifiedName}}>
+{{#model}}
+    template <> struct JsonObjectConverter<{{qualifiedName}}>
     {
-        {{qualifiedName}} operator()({{^propertyMap}}const QJsonObject&{{/propertyMap}}{{#propertyMap}}QJsonObject{{/propertyMap}} jo) const
+{{#in?}}        static void dumpTo(QJsonObject& jo, const {{qualifiedName}}& pod)
         {
-            {{qualifiedName}} result;
-{{#vars}}            result.{{nameCamelCase}} =
-                fromJson<{{dataType.qualifiedName}}>(jo.{{#propertyMap}}take{{/propertyMap}}{{^propertyMap}}value{{/propertyMap}}("{{baseName}}"_ls));
-{{/vars}}{{#propertyMap}}
-            result.{{nameCamelCase}} = fromJson<{{dataType.qualifiedName}}>(jo);{{/propertyMap}}
-            return result;
-        }
-    };
-{{/out?}}{{/model}}} // namespace QMatrixClient
+{{#propertyMap}}            fillJson(jo, pod.{{nameCamelCase}});
+            {{/propertyMap}}{{#parents}}fillJson<{{name}}>(jo, pod);
+            {{/parents}}{{#vars
+}}            addParam<{{^required?}}IfNotEmpty{{/required?}}>(jo, QStringLiteral("{{baseName}}"), pod.{{nameCamelCase}});
+{{/vars}}        }
+{{/in?}}{{#out?
+}}        static void fillFrom({{^propertyMap}}const QJsonObject&{{/propertyMap
+                             }}{{#propertyMap}}QJsonObject{{/propertyMap}} jo, {{qualifiedName}}& result)
+        {
+{{#parents}}            fillFromJson<{{qualifiedName}}{{!of the parent!}}>(jo, result);
+        {{/parents}}{{#vars
+}}            fromJson(jo.{{#propertyMap}}take{{/propertyMap
+                    }}{{^propertyMap}}value{{/propertyMap}}("{{baseName}}"_ls), result.{{nameCamelCase}});
+{{/vars}}{{#propertyMap}}            fromJson(jo, result.{{nameCamelCase}});
+{{/propertyMap}}        }
+{{/out?}}    };
+{{/model}}} // namespace QMatrixClient
 {{/    models}}{{#responses}}{{#normalResponse?}}{{#allProperties?}}
 class {{camelCaseOperationId}}Job::Private
 {
@@ -109,12 +112,12 @@ BaseJob::Status {{camelCaseOperationId}}Job::parseReply(QNetworkReply* reply)
 }{{/       producesNonJson?}}{{^producesNonJson?}}
 BaseJob::Status {{camelCaseOperationId}}Job::parseJson(const QJsonDocument& data)
 {
-{{#inlineResponse}}    d->{{paramName}} = fromJson<{{dataType.name}}>(data);
+{{#inlineResponse}}    fromJson(data, d->{{paramName}});
 {{/inlineResponse}}{{^inlineResponse}}    auto json = data.object();
 {{#properties}}{{#required?}}    if (!json.contains("{{baseName}}"_ls))
         return { JsonParseError,
             "The key '{{baseName}}' not found in the response" };
-{{/required?}}    d->{{paramName}} = fromJson<{{dataType.name}}>(json.value("{{baseName}}"_ls));
+{{/required?}}    fromJson(json.value("{{baseName}}"_ls), d->{{paramName}});
 {{/properties}}{{/inlineResponse}}    return Success;
 }{{/       producesNonJson?}}
 {{/allProperties?}}{{/normalResponse?}}{{/responses}}{{/operation}}{{/operations}}
diff --git a/lib/csapi/{{base}}.h.mustache b/lib/csapi/{{base}}.h.mustache
index 147c8607..a9c3a63a 100644
--- a/lib/csapi/{{base}}.h.mustache
+++ b/lib/csapi/{{base}}.h.mustache
@@ -18,14 +18,13 @@ namespace QMatrixClient
 {{/vars}}{{#propertyMap}}{{#description}}        /// {{_}}
 {{/description}}        {{>maybeOmittableType}} {{nameCamelCase}};
 {{/propertyMap}}    };
-{{#in?}}
-    QJsonObject toJson(const {{name}}& pod);
-{{/in?}}{{#out?}}
-    template <> struct FromJsonObject<{{name}}>
+    template <> struct JsonObjectConverter<{{name}}>
     {
-        {{name}} operator()({{^propertyMap}}const QJsonObject&{{/propertyMap}}{{#propertyMap}}QJsonObject{{/propertyMap}} jo) const;
-    };
-{{/    out?}}{{/model}}
+        {{#in?}}static void dumpTo(QJsonObject& jo, const {{name}}& pod);
+        {{/in?}}{{#out?}}static void fillFrom({{^propertyMap}}const QJsonObject&{{/propertyMap
+                           }}{{#propertyMap}}QJsonObject{{/propertyMap}} jo, {{name}}& pod);
+{{/out?}}    };
+{{/model}}
 {{/models}}{{#operations}}    // Operations
 {{#    operation}}{{#summary}}
     /// {{summary}}{{#description?}}{{!add a linebreak between summary and description if both exist}}
diff --git a/lib/events/accountdataevents.h b/lib/events/accountdataevents.h
index d1c1abc8..a99d85ac 100644
--- a/lib/events/accountdataevents.h
+++ b/lib/events/accountdataevents.h
@@ -36,37 +36,38 @@ namespace QMatrixClient
         order_type order;
 
         TagRecord (order_type order = none) : order(order) { }
-        explicit TagRecord(const QJsonObject& jo)
+
+        bool operator<(const TagRecord& other) const
+        {
+            // Per The Spec, rooms with no order should be after those with order
+            return !order.omitted() &&
+                        (other.order.omitted() || order.value() < other.order.value());
+        }
+    };
+
+    template <> struct JsonObjectConverter<TagRecord>
+    {
+        static void fillFrom(const QJsonObject& jo, TagRecord& rec)
         {
             // Parse a float both from JSON double and JSON string because
             // libqmatrixclient previously used to use strings to store order.
             const auto orderJv = jo.value("order"_ls);
             if (orderJv.isDouble())
-                order = fromJson<float>(orderJv);
-            else if (orderJv.isString())
+                rec.order = fromJson<float>(orderJv);
+            if (orderJv.isString())
             {
                 bool ok;
-                order = orderJv.toString().toFloat(&ok);
+                rec.order = orderJv.toString().toFloat(&ok);
                 if (!ok)
-                    order = none;
+                    rec.order = none;
             }
         }
-
-        bool operator<(const TagRecord& other) const
+        static void dumpTo(QJsonObject& jo, const TagRecord& rec)
         {
-            // Per The Spec, rooms with no order should be after those with order
-            return !order.omitted() &&
-                        (other.order.omitted() || order.value() < other.order.value());
+            addParam<IfNotEmpty>(jo, QStringLiteral("order"), rec.order);
         }
     };
 
-    inline QJsonValue toJson(const TagRecord& rec)
-    {
-        QJsonObject o;
-        addParam<IfNotEmpty>(o, QStringLiteral("order"), rec.order);
-        return o;
-    }
-
     using TagsMap = QHash<QString, TagRecord>;
 
 #define DEFINE_SIMPLE_EVENT(_Name, _TypeId, _ContentType, _ContentKey) \
diff --git a/lib/events/eventloader.h b/lib/events/eventloader.h
index cd2f9149..da663392 100644
--- a/lib/events/eventloader.h
+++ b/lib/events/eventloader.h
@@ -57,11 +57,15 @@ namespace QMatrixClient {
                                             matrixType);
     }
 
-    template <typename EventT> struct FromJsonObject<event_ptr_tt<EventT>>
+    template <typename EventT> struct JsonConverter<event_ptr_tt<EventT>>
     {
-        auto operator()(const QJsonObject& jo) const
+        static auto load(const QJsonValue& jv)
         {
-            return loadEvent<EventT>(jo);
+            return loadEvent<EventT>(jv.toObject());
+        }
+        static auto load(const QJsonDocument& jd)
+        {
+            return loadEvent<EventT>(jd.object());
         }
     };
 } // namespace QMatrixClient
diff --git a/lib/events/roommemberevent.cpp b/lib/events/roommemberevent.cpp
index eaa3302c..a5ac3c5f 100644
--- a/lib/events/roommemberevent.cpp
+++ b/lib/events/roommemberevent.cpp
@@ -23,20 +23,17 @@
 
 #include <array>
 
-using namespace QMatrixClient;
-
 static const std::array<QString, 5> membershipStrings = { {
     QStringLiteral("invite"), QStringLiteral("join"),
     QStringLiteral("knock"), QStringLiteral("leave"),
     QStringLiteral("ban")
 } };
 
-namespace QMatrixClient
-{
+namespace QMatrixClient {
     template <>
-    struct FromJson<MembershipType>
+    struct JsonConverter<MembershipType>
     {
-        MembershipType operator()(const QJsonValue& jv) const
+        static MembershipType load(const QJsonValue& jv)
         {
             const auto& membershipString = jv.toString();
             for (auto it = membershipStrings.begin();
@@ -48,9 +45,10 @@ namespace QMatrixClient
             return MembershipType::Undefined;
         }
     };
-
 }
 
+using namespace QMatrixClient;
+
 MemberEventContent::MemberEventContent(const QJsonObject& json)
     : membership(fromJson<MembershipType>(json["membership"_ls]))
     , isDirect(json["is_direct"_ls].toBool())
diff --git a/lib/identity/definitions/request_email_validation.cpp b/lib/identity/definitions/request_email_validation.cpp
index 95088bcb..47463a8b 100644
--- a/lib/identity/definitions/request_email_validation.cpp
+++ b/lib/identity/definitions/request_email_validation.cpp
@@ -6,28 +6,21 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const RequestEmailValidation& pod)
+void JsonObjectConverter<RequestEmailValidation>::dumpTo(
+        QJsonObject& jo, const RequestEmailValidation& pod)
 {
-    QJsonObject jo;
     addParam<>(jo, QStringLiteral("client_secret"), pod.clientSecret);
     addParam<>(jo, QStringLiteral("email"), pod.email);
     addParam<>(jo, QStringLiteral("send_attempt"), pod.sendAttempt);
     addParam<IfNotEmpty>(jo, QStringLiteral("next_link"), pod.nextLink);
-    return jo;
 }
 
-RequestEmailValidation FromJsonObject<RequestEmailValidation>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<RequestEmailValidation>::fillFrom(
+    const QJsonObject& jo, RequestEmailValidation& result)
 {
-    RequestEmailValidation result;
-    result.clientSecret =
-        fromJson<QString>(jo.value("client_secret"_ls));
-    result.email =
-        fromJson<QString>(jo.value("email"_ls));
-    result.sendAttempt =
-        fromJson<int>(jo.value("send_attempt"_ls));
-    result.nextLink =
-        fromJson<QString>(jo.value("next_link"_ls));
-
-    return result;
+    fromJson(jo.value("client_secret"_ls), result.clientSecret);
+    fromJson(jo.value("email"_ls), result.email);
+    fromJson(jo.value("send_attempt"_ls), result.sendAttempt);
+    fromJson(jo.value("next_link"_ls), result.nextLink);
 }
 
diff --git a/lib/identity/definitions/request_email_validation.h b/lib/identity/definitions/request_email_validation.h
index 3e72275f..eb7d8ed6 100644
--- a/lib/identity/definitions/request_email_validation.h
+++ b/lib/identity/definitions/request_email_validation.h
@@ -33,12 +33,10 @@ namespace QMatrixClient
         /// server will redirect the user to this URL.
         QString nextLink;
     };
-
-    QJsonObject toJson(const RequestEmailValidation& pod);
-
-    template <> struct FromJsonObject<RequestEmailValidation>
+    template <> struct JsonObjectConverter<RequestEmailValidation>
     {
-        RequestEmailValidation operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const RequestEmailValidation& pod);
+        static void fillFrom(const QJsonObject& jo, RequestEmailValidation& pod);
     };
 
 } // namespace QMatrixClient
diff --git a/lib/identity/definitions/request_msisdn_validation.cpp b/lib/identity/definitions/request_msisdn_validation.cpp
index 125baa9c..a123d326 100644
--- a/lib/identity/definitions/request_msisdn_validation.cpp
+++ b/lib/identity/definitions/request_msisdn_validation.cpp
@@ -6,31 +6,23 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const RequestMsisdnValidation& pod)
+void JsonObjectConverter<RequestMsisdnValidation>::dumpTo(
+        QJsonObject& jo, const RequestMsisdnValidation& pod)
 {
-    QJsonObject jo;
     addParam<>(jo, QStringLiteral("client_secret"), pod.clientSecret);
     addParam<>(jo, QStringLiteral("country"), pod.country);
     addParam<>(jo, QStringLiteral("phone_number"), pod.phoneNumber);
     addParam<>(jo, QStringLiteral("send_attempt"), pod.sendAttempt);
     addParam<IfNotEmpty>(jo, QStringLiteral("next_link"), pod.nextLink);
-    return jo;
 }
 
-RequestMsisdnValidation FromJsonObject<RequestMsisdnValidation>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<RequestMsisdnValidation>::fillFrom(
+    const QJsonObject& jo, RequestMsisdnValidation& result)
 {
-    RequestMsisdnValidation result;
-    result.clientSecret =
-        fromJson<QString>(jo.value("client_secret"_ls));
-    result.country =
-        fromJson<QString>(jo.value("country"_ls));
-    result.phoneNumber =
-        fromJson<QString>(jo.value("phone_number"_ls));
-    result.sendAttempt =
-        fromJson<int>(jo.value("send_attempt"_ls));
-    result.nextLink =
-        fromJson<QString>(jo.value("next_link"_ls));
-
-    return result;
+    fromJson(jo.value("client_secret"_ls), result.clientSecret);
+    fromJson(jo.value("country"_ls), result.country);
+    fromJson(jo.value("phone_number"_ls), result.phoneNumber);
+    fromJson(jo.value("send_attempt"_ls), result.sendAttempt);
+    fromJson(jo.value("next_link"_ls), result.nextLink);
 }
 
diff --git a/lib/identity/definitions/request_msisdn_validation.h b/lib/identity/definitions/request_msisdn_validation.h
index 77bea2bc..b48ed6d5 100644
--- a/lib/identity/definitions/request_msisdn_validation.h
+++ b/lib/identity/definitions/request_msisdn_validation.h
@@ -36,12 +36,10 @@ namespace QMatrixClient
         /// server will redirect the user to this URL.
         QString nextLink;
     };
-
-    QJsonObject toJson(const RequestMsisdnValidation& pod);
-
-    template <> struct FromJsonObject<RequestMsisdnValidation>
+    template <> struct JsonObjectConverter<RequestMsisdnValidation>
     {
-        RequestMsisdnValidation operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const RequestMsisdnValidation& pod);
+        static void fillFrom(const QJsonObject& jo, RequestMsisdnValidation& pod);
     };
 
 } // namespace QMatrixClient
diff --git a/lib/identity/definitions/sid.cpp b/lib/identity/definitions/sid.cpp
index 443dbedf..1ba4b3b5 100644
--- a/lib/identity/definitions/sid.cpp
+++ b/lib/identity/definitions/sid.cpp
@@ -6,19 +6,15 @@
 
 using namespace QMatrixClient;
 
-QJsonObject QMatrixClient::toJson(const Sid& pod)
+void JsonObjectConverter<Sid>::dumpTo(
+        QJsonObject& jo, const Sid& pod)
 {
-    QJsonObject jo;
     addParam<>(jo, QStringLiteral("sid"), pod.sid);
-    return jo;
 }
 
-Sid FromJsonObject<Sid>::operator()(const QJsonObject& jo) const
+void JsonObjectConverter<Sid>::fillFrom(
+    const QJsonObject& jo, Sid& result)
 {
-    Sid result;
-    result.sid =
-        fromJson<QString>(jo.value("sid"_ls));
-
-    return result;
+    fromJson(jo.value("sid"_ls), result.sid);
 }
 
diff --git a/lib/identity/definitions/sid.h b/lib/identity/definitions/sid.h
index eae60c47..ac8c4130 100644
--- a/lib/identity/definitions/sid.h
+++ b/lib/identity/definitions/sid.h
@@ -19,12 +19,10 @@ namespace QMatrixClient
         /// must not be empty.
         QString sid;
     };
-
-    QJsonObject toJson(const Sid& pod);
-
-    template <> struct FromJsonObject<Sid>
+    template <> struct JsonObjectConverter<Sid>
     {
-        Sid operator()(const QJsonObject& jo) const;
+        static void dumpTo(QJsonObject& jo, const Sid& pod);
+        static void fillFrom(const QJsonObject& jo, Sid& pod);
     };
 
 } // namespace QMatrixClient