Simplify signature of untyped property bindings

Instead of requiring the implementation to do the compare dance, let's
do this in the library. This reduces the amount of duplicated code
slightly and makes it easier to generate binding code from qml files.

Change-Id: Ia3b16cf9769e74d076b669efe4119ab84af3cdf0
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 21 insertions, 11 deletions

diff --git a/src/corelib/kernel/qpropertybinding.cpp b/src/corelib/kernel/qpropertybinding.cpp
index 358977e63e..29b1a4a69a 100644
--- a/src/corelib/kernel/qpropertybinding.cpp
+++ b/src/corelib/kernel/qpropertybinding.cpp
@@ -41,6 +41,7 @@
 #include "qproperty_p.h"
 
 #include <QScopedValueRollback>
+#include <QVariant>
 
 QT_BEGIN_NAMESPACE
 
@@ -80,25 +81,34 @@ bool QPropertyBindingPrivate::evaluateIfDirtyAndReturnTrueIfValueChanged()
 
     BindingEvaluationState evaluationFrame(this);
 
+    QPropertyBindingError evalError;
     QUntypedPropertyBinding::BindingEvaluationResult result;
     bool changed = false;
     if (metaType.id() == QMetaType::Bool) {
         auto propertyPtr = reinterpret_cast<QPropertyBase *>(propertyDataPtr);
-        bool temp = propertyPtr->extraBit();
-        result = evaluationFunction(metaType, &temp);
-        if (auto changedPtr = std::get_if<bool>(&result)) {
-            changed = *changedPtr;
-            if (changed)
-                propertyPtr->setExtraBit(temp);
+        bool newValue = false;
+        evalError = evaluationFunction(metaType, &newValue);
+        if (evalError.type() == QPropertyBindingError::NoError) {
+            if (propertyPtr->extraBit() != newValue) {
+                propertyPtr->setExtraBit(newValue);
+                changed = true;
+            }
         }
     } else {
-        result = evaluationFunction(metaType, propertyDataPtr);
-        if (auto changedPtr = std::get_if<bool>(&result))
-            changed = *changedPtr;
+        QVariant resultVariant(metaType.id(), nullptr);
+        evalError = evaluationFunction(metaType, resultVariant.data());
+        if (evalError.type() == QPropertyBindingError::NoError) {
+            int compareResult = 0;
+            if (!QMetaType::compare(propertyDataPtr, resultVariant.constData(), metaType.id(), &compareResult) || compareResult != 0) {
+                changed = true;
+                metaType.destruct(propertyDataPtr);
+                metaType.construct(propertyDataPtr, resultVariant.constData());
+            }
+        }
     }
 
-    if (auto errorPtr = std::get_if<QPropertyBindingError>(&result))
-        error = std::move(*errorPtr);
+    if (evalError.type() != QPropertyBindingError::NoError)
+        error = evalError;
 
     dirty = false;
     return changed;