QGraphicsView: replace some Q_FOREACH loops over rvalues with C++11 range-for

This needs to be handled a bit carefully, because Qt containers
will detach upon being iterated over using range-for.

In the cases of this patch, that trivially cannot happen, because
all containers are marked as const when being assigned the rvalues
previously found on the rhs of the Q_FOREACH. The new code thus
does exactly what the old code did: take a const copy, then iterate
over it.

Separate patches will deal with other situations.

Range-for loops are much more efficient than foreach loops.

This patch shaves almost 4K of text size off an optimized Linux
AMD64 GCC 4.9 build.

Change-Id: Ida868b77d078cbfa0516d17e98e6f0a86fcdb7a3
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

1 files changed, 6 insertions, 7 deletions

diff --git a/src/widgets/graphicsview/qgraphicsanchorlayout_p.cpp b/src/widgets/graphicsview/qgraphicsanchorlayout_p.cpp
index e16b427448..adc77ded47 100644
--- a/src/widgets/graphicsview/qgraphicsanchorlayout_p.cpp
+++ b/src/widgets/graphicsview/qgraphicsanchorlayout_p.cpp
@@ -2318,9 +2318,9 @@ void QGraphicsAnchorLayoutPrivate::findPaths(Orientation orientation)
 
     graphPaths[orientation].insert(root, GraphPath());
 
-    foreach (AnchorVertex *v, graph[orientation].adjacentVertices(root)) {
+    const auto adjacentVertices = graph[orientation].adjacentVertices(root);
+    for (AnchorVertex *v : adjacentVertices)
         queue.enqueue(qMakePair(root, v));
-    }
 
     while(!queue.isEmpty()) {
         QPair<AnchorVertex *, AnchorVertex *>  pair = queue.dequeue();
@@ -2339,10 +2339,9 @@ void QGraphicsAnchorLayoutPrivate::findPaths(Orientation orientation)
 
         graphPaths[orientation].insert(pair.second, current);
 
-        foreach (AnchorVertex *v,
-                graph[orientation].adjacentVertices(pair.second)) {
+        const auto adjacentVertices = graph[orientation].adjacentVertices(pair.second);
+        for (AnchorVertex *v : adjacentVertices)
             queue.enqueue(qMakePair(pair.second, v));
-        }
     }
 
     // We will walk through every reachable items (non-float) store them in a temporary set.
@@ -2703,9 +2702,9 @@ void QGraphicsAnchorLayoutPrivate::calculateVertexPositions(
     visited.insert(root);
 
     // Add initial edges to the queue
-    foreach (AnchorVertex *v, graph[orientation].adjacentVertices(root)) {
+    const auto adjacentVertices = graph[orientation].adjacentVertices(root);
+    for (AnchorVertex *v : adjacentVertices)
         queue.enqueue(qMakePair(root, v));
-    }
 
     // Do initial calculation required by "interpolateEdge()"
     setupEdgesInterpolation(orientation);