1 files changed, 35 insertions, 8 deletions
diff --git a/src/corelib/json/qjsonobject.cpp b/src/corelib/json/qjsonobject.cpp
index 27e51cf4ac..cfd797990f 100644
--- a/src/corelib/json/qjsonobject.cpp
+++ b/src/corelib/json/qjsonobject.cpp
@@ -116,6 +116,20 @@ QJsonObject::QJsonObject()
 }
 
 /*!
+    \fn QJsonObject::QJsonObject(std::initializer_list<QPair<QString, QJsonValue> > args)
+    \since 5.4
+    Constructs a QJsonObject instance initialized from \a args initialization list.
+    For example:
+    \code
+    QJsonObject object
+    {
+        {"property1", 1},
+        {"property2", 2}
+    };
+    \endcode
+*/
+
+/*!
     \internal
  */
 QJsonObject::QJsonObject(QJsonPrivate::Data *data, QJsonPrivate::Object *object)
@@ -126,6 +140,19 @@ QJsonObject::QJsonObject(QJsonPrivate::Data *data, QJsonPrivate::Object *object)
     d->ref.ref();
 }
 
+/*!
+    This method replaces part of the QJsonObject(std::initializer_list<QPair<QString, QJsonValue>> args) body.
+    The constructor needs to be inline, but we do not want to leak implementation details
+    of this class.
+    \note this method is called for an uninitialized object
+    \internal
+ */
+
+void QJsonObject::initialize()
+{
+    d = 0;
+    o = 0;
+}
 
 /*!
     Destroys the object.
@@ -134,6 +161,7 @@ QJsonObject::~QJsonObject()
 {
     if (d && !d->ref.deref())
         delete d;
+    QJsonPrivate::ObjectUndefinedKeys::removeKeys(this); // ### Qt6 move it to ~QJsonValueRef
 }
 
 /*!
@@ -254,7 +282,7 @@ bool QJsonObject::isEmpty() const
 QJsonValue QJsonObject::value(const QString &key) const
 {
     if (!d)
-        return QJsonValue();
+        return QJsonValue(QJsonValue::Undefined);
 
     bool keyExists;
     int i = o->indexOf(key, &keyExists);
@@ -290,14 +318,9 @@ QJsonValue QJsonObject::operator [](const QString &key) const
  */
 QJsonValueRef QJsonObject::operator [](const QString &key)
 {
-    // ### somewhat inefficient, as we lookup the key twice if it doesn't yet exist
     bool keyExists = false;
     int index = o ? o->indexOf(key, &keyExists) : -1;
-    if (!keyExists) {
-        iterator i = insert(key, QJsonValue());
-        index = i.i;
-    }
-    return QJsonValueRef(this, index);
+    return keyExists ? QJsonValueRef(this, index) : QJsonValueRef(this, key);
 }
 
 /*!
@@ -1001,7 +1024,9 @@ void QJsonObject::compact()
 
     detach();
     d->compact();
-    o = static_cast<QJsonPrivate::Object *>(d->header->root());
+    using namespace QJsonPrivate;
+    o = static_cast<Object *>(d->header->root());
+    ObjectUndefinedKeys::removeKeys(this); // ### Qt6 move it to ~QJsonValueRef
 }
 
 /*!
@@ -1038,6 +1063,8 @@ void QJsonObject::setValueAt(int i, const QJsonValue &val)
     insert(e->key(), val);
 }
 
+QBasicMutex QJsonPrivate::ObjectUndefinedKeys::mutex;
+
 #if !defined(QT_NO_DEBUG_STREAM) && !defined(QT_JSON_READONLY)
 QDebug operator<<(QDebug dbg, const QJsonObject &o)
 {