Derive Omittable<> from std::optional<>

That breaks API all over the place but:
1. The fixes are trivial.
2. More of std:: is used instead of home-baking the same stuff.

10 files changed, 81 insertions, 536 deletions

diff --git a/lib/connection.cpp b/lib/connection.cpp
index 3d617733..47c643b0 100644
--- a/lib/connection.cpp
+++ b/lib/connection.cpp
@@ -277,16 +277,16 @@ void Connection::reloadCapabilities()
         else if (d->capabilitiesJob->error() == BaseJob::IncorrectRequestError)
             qCDebug(MAIN) << "Server doesn't support /capabilities";
 
-        if (d->capabilities.roomVersions.omitted()) {
+        if (!d->capabilities.roomVersions) {
             qCWarning(MAIN) << "Pinning supported room version to 1";
-            d->capabilities.roomVersions = { "1", { { "1", "stable" } } };
+            d->capabilities.roomVersions.emplace({ "1", { { "1", "stable" } } });
         } else {
             qCDebug(MAIN) << "Room versions:" << defaultRoomVersion()
                           << "is default, full list:" << availableRoomVersions();
         }
-        Q_ASSERT(!d->capabilities.roomVersions.omitted());
+        Q_ASSERT(d->capabilities.roomVersions.has_value());
         emit capabilitiesLoaded();
-        for (auto* r : d->roomMap)
+        for (auto* r : qAsConst(d->roomMap))
             r->checkVersion();
     });
 }
@@ -295,7 +295,7 @@ bool Connection::loadingCapabilities() const
 {
     // (Ab)use the fact that room versions cannot be omitted after
     // the capabilities have been loaded (see reloadCapabilities() above).
-    return d->capabilities.roomVersions.omitted();
+    return !d->capabilities.roomVersions;
 }
 
 void Connection::Private::connectWithToken(const QString& userId,
@@ -363,8 +363,8 @@ void Connection::sync(int timeout)
 
     d->syncTimeout = timeout;
     Filter filter;
-    filter.room->timeline->limit = 100;
-    filter.room->state->lazyLoadMembers = d->lazyLoading;
+    filter.room.edit().timeline.edit().limit.emplace(100);
+    filter.room.edit().state.edit().lazyLoadMembers.emplace(d->lazyLoading);
     auto job = d->syncJob =
         callApi<SyncJob>(BackgroundRequest, d->data->lastEvent(), filter,
                          timeout);
@@ -446,7 +446,7 @@ void Connection::onSyncSuccess(SyncData&& data, bool fromCache)
             r->updateData(std::move(roomData), fromCache);
             if (d->firstTimeRooms.removeOne(r)) {
                 emit loadedRoomState(r);
-                if (!d->capabilities.roomVersions.omitted())
+                if (d->capabilities.roomVersions)
                     r->checkVersion();
                 // Otherwise, the version will be checked in reloadCapabilities()
             }
@@ -1191,7 +1191,7 @@ Room* Connection::provideRoom(const QString& id, Omittable<JoinState> joinState)
         // and emit a signal. For Invite and Join, there's no such problem.
         if (room->joinState() == joinState && joinState != JoinState::Leave)
             return room;
-    } else if (joinState.omitted()) {
+    } else if (!joinState) {
         // No Join and Leave, maybe Invite?
         room = d->roomMap.value({ id, true }, nullptr);
         if (room)
@@ -1200,9 +1200,7 @@ Room* Connection::provideRoom(const QString& id, Omittable<JoinState> joinState)
     }
 
     if (!room) {
-        room = roomFactory()(this, id,
-                             joinState.omitted() ? JoinState::Join
-                                                 : joinState.value());
+        room = roomFactory()(this, id, joinState.value_or(JoinState::Join));
         if (!room) {
             qCCritical(MAIN) << "Failed to create a room" << id;
             return nullptr;
@@ -1213,7 +1211,7 @@ Room* Connection::provideRoom(const QString& id, Omittable<JoinState> joinState)
                 &Connection::aboutToDeleteRoom);
         emit newRoom(room);
     }
-    if (joinState.omitted())
+    if (!joinState)
         return room;
 
     if (joinState == JoinState::Invite) {
@@ -1431,13 +1429,13 @@ const QString Connection::SupportedRoomVersion::StableTag =
 
 QString Connection::defaultRoomVersion() const
 {
-    Q_ASSERT(!d->capabilities.roomVersions.omitted());
+    Q_ASSERT(d->capabilities.roomVersions.has_value());
     return d->capabilities.roomVersions->defaultVersion;
 }
 
 QStringList Connection::stableRoomVersions() const
 {
-    Q_ASSERT(!d->capabilities.roomVersions.omitted());
+    Q_ASSERT(d->capabilities.roomVersions.has_value());
     QStringList l;
     const auto& allVersions = d->capabilities.roomVersions->available;
     for (auto it = allVersions.begin(); it != allVersions.end(); ++it)
@@ -1457,7 +1455,7 @@ inline bool roomVersionLess(const Connection::SupportedRoomVersion& v1,
 
 QVector<Connection::SupportedRoomVersion> Connection::availableRoomVersions() const
 {
-    Q_ASSERT(!d->capabilities.roomVersions.omitted());
+    Q_ASSERT(d->capabilities.roomVersions.has_value());
     QVector<SupportedRoomVersion> result;
     result.reserve(d->capabilities.roomVersions->available.size());
     for (auto it = d->capabilities.roomVersions->available.begin();
diff --git a/lib/converters.h b/lib/converters.h
index b753a80b..157bff27 100644
--- a/lib/converters.h
+++ b/lib/converters.h
@@ -206,7 +206,7 @@ template <typename T>
 struct JsonConverter<Omittable<T>> {
     static QJsonValue dump(const Omittable<T>& from)
     {
-        return from.omitted() ? QJsonValue() : toJson(from.value());
+        return from.has_value() ? toJson(from.value()) : QJsonValue();
     }
     static Omittable<T> load(const QJsonValue& jv)
     {
@@ -378,28 +378,10 @@ namespace _impl {
         static void impl(ContT& container, const QString& key,
                          const OmittableT& value)
         {
-            if (!value.omitted())
-                addTo(container, key, value.value());
+            if (value)
+                addTo(container, key, *value);
         }
     };
-
-#if 0
-        // This is a special one that unfolds optional<>
-        template <typename ValT, bool Force>
-        struct AddNode<optional<ValT>, Force>
-        {
-            template <typename ContT, typename OptionalT>
-            static void impl(ContT& container,
-                             const QString& key, const OptionalT& value)
-            {
-                if (value)
-                    AddNode<ValT>::impl(container, key, value.value());
-                else if (Force) // Edge case, no value but must put something
-                    AddNode<ValT>::impl(container, key, QString{});
-            }
-        };
-#endif
-
 } // namespace _impl
 
 static constexpr bool IfNotEmpty = false;
diff --git a/lib/csapi/search.cpp b/lib/csapi/search.cpp
deleted file mode 100644
index 9619f340..00000000
--- a/lib/csapi/search.cpp
+++ /dev/null
@@ -1,191 +0,0 @@
-/******************************************************************************
- * THIS FILE IS GENERATED - ANY EDITS WILL BE OVERWRITTEN
- */
-
-#include "search.h"
-
-#include "converters.h"
-
-#include <QtCore/QStringBuilder>
-
-using namespace Quotient;
-
-static const auto basePath = QStringLiteral("/_matrix/client/r0");
-
-// Converters
-namespace Quotient
-{
-
-template <>
-struct JsonObjectConverter<SearchJob::IncludeEventContext>
-{
-    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);
-    }
-};
-
-template <>
-struct JsonObjectConverter<SearchJob::Group>
-{
-    static void dumpTo(QJsonObject& jo, const SearchJob::Group& pod)
-    {
-        addParam<IfNotEmpty>(jo, QStringLiteral("key"), pod.key);
-    }
-};
-
-template <>
-struct JsonObjectConverter<SearchJob::Groupings>
-{
-    static void dumpTo(QJsonObject& jo, const SearchJob::Groupings& pod)
-    {
-        addParam<IfNotEmpty>(jo, QStringLiteral("group_by"), pod.groupBy);
-    }
-};
-
-template <>
-struct JsonObjectConverter<SearchJob::RoomEventsCriteria>
-{
-    static void dumpTo(QJsonObject& jo, const SearchJob::RoomEventsCriteria& pod)
-    {
-        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);
-    }
-};
-
-template <>
-struct JsonObjectConverter<SearchJob::Categories>
-{
-    static void dumpTo(QJsonObject& jo, const SearchJob::Categories& pod)
-    {
-        addParam<IfNotEmpty>(jo, QStringLiteral("room_events"), pod.roomEvents);
-    }
-};
-
-template <>
-struct JsonObjectConverter<SearchJob::UserProfile>
-{
-    static void fillFrom(const QJsonObject& jo, SearchJob::UserProfile& result)
-    {
-        fromJson(jo.value("displayname"_ls), result.displayname);
-        fromJson(jo.value("avatar_url"_ls), result.avatarUrl);
-    }
-};
-
-template <>
-struct JsonObjectConverter<SearchJob::EventContext>
-{
-    static void fillFrom(const QJsonObject& jo, SearchJob::EventContext& 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 JsonObjectConverter<SearchJob::Result>
-{
-    static void fillFrom(const QJsonObject& jo, SearchJob::Result& result)
-    {
-        fromJson(jo.value("rank"_ls), result.rank);
-        fromJson(jo.value("result"_ls), result.result);
-        fromJson(jo.value("context"_ls), result.context);
-    }
-};
-
-template <>
-struct JsonObjectConverter<SearchJob::GroupValue>
-{
-    static void fillFrom(const QJsonObject& jo, SearchJob::GroupValue& 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 JsonObjectConverter<SearchJob::ResultRoomEvents>
-{
-    static void fillFrom(const QJsonObject& jo,
-                         SearchJob::ResultRoomEvents& result)
-    {
-        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);
-    }
-};
-
-template <>
-struct JsonObjectConverter<SearchJob::ResultCategories>
-{
-    static void fillFrom(const QJsonObject& jo,
-                         SearchJob::ResultCategories& result)
-    {
-        fromJson(jo.value("room_events"_ls), result.roomEvents);
-    }
-};
-
-} // namespace Quotient
-
-class SearchJob::Private
-{
-public:
-    ResultCategories searchCategories;
-};
-
-BaseJob::Query queryToSearch(const QString& nextBatch)
-{
-    BaseJob::Query _q;
-    addParam<IfNotEmpty>(_q, QStringLiteral("next_batch"), nextBatch);
-    return _q;
-}
-
-static const auto SearchJobName = QStringLiteral("SearchJob");
-
-SearchJob::SearchJob(const Categories& searchCategories,
-                     const QString& nextBatch)
-    : BaseJob(HttpVerb::Post, SearchJobName, basePath % "/search",
-              queryToSearch(nextBatch))
-    , d(new Private)
-{
-    QJsonObject _data;
-    addParam<>(_data, QStringLiteral("search_categories"), searchCategories);
-    setRequestData(_data);
-}
-
-SearchJob::~SearchJob() = default;
-
-const SearchJob::ResultCategories& SearchJob::searchCategories() const
-{
-    return d->searchCategories;
-}
-
-BaseJob::Status SearchJob::parseJson(const QJsonDocument& data)
-{
-    auto json = data.object();
-    if (!json.contains("search_categories"_ls))
-        return { IncorrectResponse,
-                 "The key 'search_categories' not found in the response" };
-    fromJson(json.value("search_categories"_ls), d->searchCategories);
-
-    return Success;
-}
diff --git a/lib/csapi/search.h b/lib/csapi/search.h
deleted file mode 100644
index 079ac8e9..00000000
--- a/lib/csapi/search.h
+++ /dev/null
@@ -1,203 +0,0 @@
-/******************************************************************************
- * THIS FILE IS GENERATED - ANY EDITS WILL BE OVERWRITTEN
- */
-
-#pragma once
-
-#include "converters.h"
-
-#include "csapi/definitions/room_event_filter.h"
-
-#include "events/eventloader.h"
-#include "jobs/basejob.h"
-
-#include <QtCore/QHash>
-#include <QtCore/QVector>
-
-#include <unordered_map>
-
-namespace Quotient
-{
-
-// Operations
-
-/// Perform a server-side search.
-/*!
- * Performs a full text search across different categories.
- */
-class SearchJob : public BaseJob
-{
-public:
-    // Inner data structures
-
-    /// Configures whether any context for the eventsreturned are included in
-    /// the response.
-    struct IncludeEventContext
-    {
-        /// How many events before the result arereturned. By default, this is
-        /// ``5``.
-        Omittable<int> beforeLimit;
-        /// How many events after the result arereturned. By default, this is
-        /// ``5``.
-        Omittable<int> afterLimit;
-        /// Requests that the server returns thehistoric profile information for
-        /// the usersthat sent the events that were returned.By default, this is
-        /// ``false``.
-        Omittable<bool> includeProfile;
-    };
-
-    /// Configuration for group.
-    struct Group
-    {
-        /// Key that defines the group.
-        QString key;
-    };
-
-    /// Requests that the server partitions the result setbased on the provided
-    /// list of keys.
-    struct Groupings
-    {
-        /// List of groups to request.
-        QVector<Group> groupBy;
-    };
-
-    /// Mapping of category name to search criteria.
-    struct RoomEventsCriteria
-    {
-        /// The string to search events for
-        QString searchTerm;
-        /// The keys to search. Defaults to all.
-        QStringList keys;
-        /// This takes a `filter`_.
-        Omittable<RoomEventFilter> filter;
-        /// The order in which to search for results.By default, this is
-        /// ``"rank"``.
-        QString orderBy;
-        /// Configures whether any context for the eventsreturned are included
-        /// in the response.
-        Omittable<IncludeEventContext> eventContext;
-        /// Requests the server return the current state foreach room returned.
-        Omittable<bool> includeState;
-        /// Requests that the server partitions the result setbased on the
-        /// provided list of keys.
-        Omittable<Groupings> groupings;
-    };
-
-    /// Describes which categories to search in and their criteria.
-    struct Categories
-    {
-        /// Mapping of category name to search criteria.
-        Omittable<RoomEventsCriteria> roomEvents;
-    };
-
-    /// Performs a full text search across different categories.
-    struct UserProfile
-    {
-        /// Performs a full text search across different categories.
-        QString displayname;
-        /// Performs a full text search across different categories.
-        QString avatarUrl;
-    };
-
-    /// Context for result, if requested.
-    struct EventContext
-    {
-        /// Pagination token for the start of the chunk
-        QString begin;
-        /// Pagination token for the end of the chunk
-        QString end;
-        /// The historic profile information of theusers that sent the events
-        /// returned.The ``string`` key is the user ID for whichthe profile
-        /// belongs to.
-        QHash<QString, UserProfile> profileInfo;
-        /// Events just before the result.
-        RoomEvents eventsBefore;
-        /// Events just after the result.
-        RoomEvents eventsAfter;
-    };
-
-    /// The result object.
-    struct Result
-    {
-        /// A number that describes how closely this result matches the search.
-        /// Higher is closer.
-        Omittable<double> rank;
-        /// The event that matched.
-        RoomEventPtr result;
-        /// Context for result, if requested.
-        Omittable<EventContext> context;
-    };
-
-    /// The results for a particular group value.
-    struct GroupValue
-    {
-        /// Token that can be used to get the next batchof results in the group,
-        /// by passing as the`next_batch` parameter to the next call. Ifthis
-        /// field is absent, there are no moreresults in this group.
-        QString nextBatch;
-        /// Key that can be used to order differentgroups.
-        Omittable<int> order;
-        /// Which results are in this group.
-        QStringList results;
-    };
-
-    /// Mapping of category name to search criteria.
-    struct ResultRoomEvents
-    {
-        /// An approximate count of the total number of results found.
-        Omittable<int> count;
-        /// List of words which should be highlighted, useful for stemming which
-        /// may change the query terms.
-        QStringList highlights;
-        /// List of results in the requested order.
-        std::vector<Result> results;
-        /// The current state for every room in the results.This is included if
-        /// the request had the``include_state`` key set with a value of
-        /// ``true``.The ``string`` key is the room ID for which the
-        /// ``StateEvent`` array belongs to.
-        std::unordered_map<QString, StateEvents> state;
-        /// Any groups that were requested.The outer ``string`` key is the group
-        /// key requested (eg: ``room_id``or ``sender``). The inner ``string``
-        /// key is the grouped value (eg: a room's ID or a user's ID).
-        QHash<QString, QHash<QString, GroupValue>> groups;
-        /// Token that can be used to get the next batch ofresults, by passing
-        /// as the `next_batch` parameter tothe next call. If this field is
-        /// absent, there are nomore results.
-        QString nextBatch;
-    };
-
-    /// Describes which categories to search in and their criteria.
-    struct ResultCategories
-    {
-        /// Mapping of category name to search criteria.
-        Omittable<ResultRoomEvents> roomEvents;
-    };
-
-    // Construction/destruction
-
-    /*! Perform a server-side search.
-     * \param searchCategories
-     *   Describes which categories to search in and their criteria.
-     * \param nextBatch
-     *   The point to return events from. If given, this should be a
-     *   ``next_batch`` result from a previous call to this endpoint.
-     */
-    explicit SearchJob(const Categories& searchCategories,
-                       const QString& nextBatch = {});
-
-    ~SearchJob() override;
-
-    // Result properties
-
-    /// Describes which categories to search in and their criteria.
-    const ResultCategories& searchCategories() const;
-
-protected:
-    Status parseJson(const QJsonDocument& data) override;
-
-private:
-    class Private;
-    QScopedPointer<Private> d;
-};
-
-} // namespace Quotient
diff --git a/lib/events/accountdataevents.h b/lib/events/accountdataevents.h
index 31176766..a55016d9 100644
--- a/lib/events/accountdataevents.h
+++ b/lib/events/accountdataevents.h
@@ -1,5 +1,3 @@
-#include <utility>
-
 /******************************************************************************
  * Copyright (C) 2018 Kitsune Ral <kitsune-ral@users.sf.net>
  *
@@ -34,13 +32,13 @@ struct TagRecord {
 
     order_type order;
 
-    TagRecord(order_type order = none) : order(order) {}
+    TagRecord(order_type order = none) : order(std::move(order)) {}
 
     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());
+        // Per The Spec, rooms with no order should be after those with order,
+        // against optional<>::operator<() convention.
+        return order && (!other.order || *order < *other.order);
     }
 };
 
diff --git a/lib/events/roommessageevent.cpp b/lib/events/roommessageevent.cpp
index 09562d65..078ae70a 100644
--- a/lib/events/roommessageevent.cpp
+++ b/lib/events/roommessageevent.cpp
@@ -95,6 +95,11 @@ MsgType jsonToMsgType(const QString& matrixType)
     return MsgType::Unknown;
 }
 
+inline bool isReplacement(const Omittable<RelatesTo>& rel)
+{
+    return rel && rel->type == RelatesTo::ReplacementTypeId();
+}
+
 QJsonObject RoomMessageEvent::assembleContentJson(const QString& plainBody,
                                                   const QString& jsonMsgType,
                                                   TypedBase* content)
@@ -111,6 +116,7 @@ QJsonObject RoomMessageEvent::assembleContentJson(const QString& plainBody,
             // After the above, we know for sure that the content is TextContent
             // and that its RelatesTo structure is not omitted
             auto* textContent = static_cast<const TextContent*>(content);
+            Q_ASSERT(textContent && textContent->relatesTo.has_value());
             if (textContent->relatesTo->type == RelatesTo::ReplacementTypeId()) {
                 auto newContentJson = json.take("m.new_content"_ls).toObject();
                 newContentJson.insert(BodyKey, plainBody);
@@ -243,9 +249,7 @@ QString RoomMessageEvent::replacedEvent() const
         return {};
 
     const auto& rel = static_cast<const TextContent*>(content())->relatesTo;
-    return !rel.omitted() && rel->type == RelatesTo::ReplacementTypeId()
-               ? rel->eventId
-               : QString();
+    return isReplacement(rel) ? rel->eventId : QString();
 }
 
 QString rawMsgTypeForMimeType(const QMimeType& mimeType)
@@ -269,10 +273,10 @@ QString RoomMessageEvent::rawMsgTypeForFile(const QFileInfo& fi)
     return rawMsgTypeForMimeType(QMimeDatabase().mimeTypeForFile(fi));
 }
 
-TextContent::TextContent(const QString& text, const QString& contentType,
+TextContent::TextContent(QString text, const QString& contentType,
                          Omittable<RelatesTo> relatesTo)
     : mimeType(QMimeDatabase().mimeTypeForName(contentType))
-    , body(text)
+    , body(std::move(text))
     , relatesTo(std::move(relatesTo))
 {
     if (contentType == HtmlContentTypeId)
@@ -304,10 +308,9 @@ TextContent::TextContent(const QJsonObject& json)
     static const auto PlainTextMimeType = db.mimeTypeForName("text/plain");
     static const auto HtmlMimeType = db.mimeTypeForName("text/html");
 
-    const auto actualJson =
-        relatesTo.omitted() || relatesTo->type != RelatesTo::ReplacementTypeId()
-            ? json
-            : json.value("m.new_content"_ls).toObject();
+    const auto actualJson = isReplacement(relatesTo)
+                                ? json.value("m.new_content"_ls).toObject()
+                                : json;
     // Special-casing the custom matrix.org's (actually, Riot's) way
     // of sending HTML messages.
     if (actualJson["format"_ls].toString() == HtmlContentTypeId) {
@@ -331,7 +334,7 @@ void TextContent::fillJson(QJsonObject* json) const
         json->insert(FormatKey, HtmlContentTypeId);
         json->insert(FormattedBodyKey, body);
     }
-    if (!relatesTo.omitted()) {
+    if (relatesTo) {
         json->insert(QStringLiteral("m.relates_to"),
                      QJsonObject { { relatesTo->type, relatesTo->eventId } });
         if (relatesTo->type == RelatesTo::ReplacementTypeId()) {
diff --git a/lib/events/roommessageevent.h b/lib/events/roommessageevent.h
index e95aabfc..ded5e572 100644
--- a/lib/events/roommessageevent.h
+++ b/lib/events/roommessageevent.h
@@ -114,7 +114,7 @@ namespace EventContent {
      */
     class TextContent : public TypedBase {
     public:
-        TextContent(const QString& text, const QString& contentType,
+        TextContent(QString text, const QString& contentType,
                     Omittable<RelatesTo> relatesTo = none);
         explicit TextContent(const QJsonObject& json);
 
diff --git a/lib/room.cpp b/lib/room.cpp
index c4cdac04..b34c36ea 100644
--- a/lib/room.cpp
+++ b/lib/room.cpp
@@ -1201,15 +1201,13 @@ QString Room::decryptMessage(QByteArray cipher, const QString& senderKey,
 
 int Room::joinedCount() const
 {
-    return d->summary.joinedMemberCount.omitted()
-               ? d->membersMap.size()
-               : d->summary.joinedMemberCount.value();
+    return d->summary.joinedMemberCount.value_or(d->membersMap.size());
 }
 
 int Room::invitedCount() const
 {
     // TODO: Store invited users in Room too
-    Q_ASSERT(!d->summary.invitedMemberCount.omitted());
+    Q_ASSERT(d->summary.invitedMemberCount.has_value());
     return d->summary.invitedMemberCount.value();
 }
 
@@ -2620,9 +2618,8 @@ QString Room::Private::calculateDisplayname() const
     const bool emptyRoom =
         membersMap.isEmpty()
         || (membersMap.size() == 1 && isLocalUser(*membersMap.begin()));
-    const bool nonEmptySummary =
-        !summary.heroes.omitted() && !summary.heroes->empty();
-    auto shortlist = nonEmptySummary ? buildShortlist(summary.heroes.value())
+    const bool nonEmptySummary = summary.heroes && !summary.heroes->empty();
+    auto shortlist = nonEmptySummary ? buildShortlist(*summary.heroes)
                                      : !emptyRoom ? buildShortlist(membersMap)
                                                   : users_shortlist_t {};
 
diff --git a/lib/syncdata.cpp b/lib/syncdata.cpp
index 5b47b30f..89c512a2 100644
--- a/lib/syncdata.cpp
+++ b/lib/syncdata.cpp
@@ -30,8 +30,7 @@ const QString SyncRoomData::UnreadCountKey =
 
 bool RoomSummary::isEmpty() const
 {
-    return joinedMemberCount.omitted() && invitedMemberCount.omitted()
-           && heroes.omitted();
+    return !joinedMemberCount && !invitedMemberCount && !heroes;
 }
 
 bool RoomSummary::merge(const RoomSummary& other)
@@ -46,12 +45,12 @@ QDebug Quotient::operator<<(QDebug dbg, const RoomSummary& rs)
 {
     QDebugStateSaver _(dbg);
     QStringList sl;
-    if (!rs.joinedMemberCount.omitted())
-        sl << QStringLiteral("joined: %1").arg(rs.joinedMemberCount.value());
-    if (!rs.invitedMemberCount.omitted())
-        sl << QStringLiteral("invited: %1").arg(rs.invitedMemberCount.value());
-    if (!rs.heroes.omitted())
-        sl << QStringLiteral("heroes: [%1]").arg(rs.heroes.value().join(','));
+    if (rs.joinedMemberCount)
+        sl << QStringLiteral("joined: %1").arg(*rs.joinedMemberCount);
+    if (rs.invitedMemberCount)
+        sl << QStringLiteral("invited: %1").arg(*rs.invitedMemberCount);
+    if (rs.heroes)
+        sl << QStringLiteral("heroes: [%1]").arg(rs.heroes->join(','));
     dbg.nospace().noquote() << sl.join(QStringLiteral("; "));
     return dbg;
 }
diff --git a/lib/util.h b/lib/util.h
index f7a81b2a..b7bb8d4c 100644
--- a/lib/util.h
+++ b/lib/util.h
@@ -24,6 +24,7 @@
 #include <functional>
 #include <memory>
 #include <unordered_map>
+#include <optional>
 
 // Along the lines of Q_DISABLE_COPY - the upstream version comes in Qt 5.13
 #define DISABLE_MOVE(_ClassName)               \
@@ -43,68 +44,35 @@ struct HashQ {
 template <typename KeyT, typename ValT>
 using UnorderedMap = std::unordered_map<KeyT, ValT, HashQ<KeyT>>;
 
-struct NoneTag {};
-constexpr NoneTag none {};
+inline constexpr auto none = std::nullopt;
 
-/** A crude substitute for `optional` while we're not C++17
+/** `std::optional` with tweaks
  *
- * Only works with default-constructible types.
+ * Due to tweaks, only works with default-constructible types.
  */
 template <typename T>
-class Omittable {
+class Omittable : public std::optional<T> {
     static_assert(!std::is_reference<T>::value,
                   "You cannot make an Omittable<> with a reference type");
 
 public:
     using value_type = std::decay_t<T>;
+    static_assert(std::is_default_constructible_v<value_type>,
+                  "Omittable<> requires a default-constructible type");
 
-    explicit Omittable() : Omittable(none) {}
-    Omittable(NoneTag) : _value(value_type()), _omitted(true) {}
-    Omittable(const value_type& val) : _value(val) {}
-    Omittable(value_type&& val) : _value(std::move(val)) {}
-    Omittable<T>& operator=(const value_type& val)
-    {
-        _value = val;
-        _omitted = false;
-        return *this;
-    }
-    Omittable<T>& operator=(value_type&& val)
-    {
-        // For some reason GCC complains about -Wmaybe-uninitialized
-        // in the context of using Omittable<bool> with converters.h;
-        // though the logic looks very much benign (GCC bug???)
-        _value = std::move(val);
-        _omitted = false;
-        return *this;
-    }
+    using std::optional<T>::optional;
 
-    bool operator==(const value_type& rhs) const
-    {
-        return !omitted() && value() == rhs;
-    }
-    friend bool operator==(const value_type& lhs,
-                           const Omittable<value_type>& rhs)
-    {
-        return rhs == lhs;
-    }
-    bool operator!=(const value_type& rhs) const { return !operator==(rhs); }
-    friend bool operator!=(const value_type& lhs,
-                           const Omittable<value_type>& rhs)
-    {
-        return !(rhs == lhs);
-    }
+    // Overload emplace() to allow passing braced-init-lists (the standard
+    // emplace() does direct-initialisation but not direct-list-initialisation).
+    using std::optional<T>::emplace;
+    T& emplace(const T& val) { return std::optional<T>::emplace(val); }
+    T& emplace(T&& val) { return std::optional<T>::emplace(std::move(val)); }
 
-    bool omitted() const { return _omitted; }
-    const value_type& value() const
-    {
-        Q_ASSERT(!_omitted);
-        return _value;
-    }
-    value_type& editValue()
+    value_type& edit()
     {
-        _omitted = false;
-        return _value;
+        return this->has_value() ? this->value() : this->emplace();
     }
+
     /// Merge the value from another Omittable
     /// \return true if \p other is not omitted and the value of
     ///         the current Omittable was different (or omitted);
@@ -114,26 +82,20 @@ public:
     auto merge(const Omittable<T1>& other)
         -> std::enable_if_t<std::is_convertible<T1, T>::value, bool>
     {
-        if (other.omitted() || (!_omitted && _value == other.value()))
+        if (!other || (this->has_value() && **this == *other))
             return false;
-        _omitted = false;
-        _value = other.value();
+        *this = other;
         return true;
     }
-    value_type&& release()
-    {
-        _omitted = true;
-        return std::move(_value);
-    }
 
-    const value_type* operator->() const& { return &value(); }
-    value_type* operator->() & { return &editValue(); }
-    const value_type& operator*() const& { return value(); }
-    value_type& operator*() & { return editValue(); }
+    // Hide non-const lvalue operator-> and operator* as these are
+    // a bit too surprising: value() & doesn't lazy-create an object;
+    // and it's too easy to inadvertently change the underlying value.
 
-private:
-    T _value;
-    bool _omitted = false;
+    const value_type* operator->() const& { return &this->value(); }
+    value_type* operator->() && { return &this->value(); }
+    const value_type& operator*() const& { return this->value(); }
+    value_type& operator*() && { return this->value(); }
 };
 
 namespace _impl {
@@ -213,19 +175,19 @@ class Range {
     using size_type = typename ArrayT::size_type;
 
 public:
-    Range(ArrayT& arr) : from(std::begin(arr)), to(std::end(arr)) {}
-    Range(iterator from, iterator to) : from(from), to(to) {}
+    constexpr Range(ArrayT& arr) : from(std::begin(arr)), to(std::end(arr)) {}
+    constexpr Range(iterator from, iterator to) : from(from), to(to) {}
 
-    size_type size() const
+    constexpr size_type size() const
     {
         Q_ASSERT(std::distance(from, to) >= 0);
         return size_type(std::distance(from, to));
     }
-    bool empty() const { return from == to; }
-    const_iterator begin() const { return from; }
-    const_iterator end() const { return to; }
-    iterator begin() { return from; }
-    iterator end() { return to; }
+    constexpr bool empty() const { return from == to; }
+    constexpr const_iterator begin() const { return from; }
+    constexpr const_iterator end() const { return to; }
+    constexpr iterator begin() { return from; }
+    constexpr iterator end() { return to; }
 
 private:
     iterator from;
@@ -239,8 +201,8 @@ private:
  */
 template <typename InputIt, typename ForwardIt, typename Pred>
 inline std::pair<InputIt, ForwardIt> findFirstOf(InputIt first, InputIt last,
-                                                 ForwardIt sFirst,
-                                                 ForwardIt sLast, Pred pred)
+                                                    ForwardIt sFirst,
+                                                    ForwardIt sLast, Pred pred)
 {
     for (; first != last; ++first)
         for (auto it = sFirst; it != sLast; ++it)