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.

6 files changed, 52 insertions, 94 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