QtWidgets: prevent detach attempts from first()/etc. use [dialogs, kernel, util, widgets]

The algorithm used was:
- If possible, just declare the container const
- Otherwise, for first()/last(), use constFirst()/constLast()
  and for front()/back(), to not destroy the use of the STL
  API subset, use qAsConst()

Did some caching of function returns here and there, and
converted one 0 to nullptr as a drive-by.

Also saves almost 4KiB in text size on optimized GCC 4.9
Linux AMD64 builds.

Change-Id: I04b7bfd68dc85c22de247cb65a310e1cbbca1e8c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/src/widgets/util/qundostack.cpp b/src/widgets/util/qundostack.cpp
index 6643b4429c..6f733f99d5 100644
--- a/src/widgets/util/qundostack.cpp
+++ b/src/widgets/util/qundostack.cpp
@@ -588,9 +588,9 @@ void QUndoStack::push(QUndoCommand *cmd)
 
     QUndoCommand *cur = 0;
     if (macro) {
-        QUndoCommand *macro_cmd = d->macro_stack.last();
+        QUndoCommand *macro_cmd = d->macro_stack.constLast();
         if (!macro_cmd->d->child_list.isEmpty())
-            cur = macro_cmd->d->child_list.last();
+            cur = macro_cmd->d->child_list.constLast();
     } else {
         if (d->index > 0)
             cur = d->command_list.at(d->index - 1);
@@ -616,7 +616,7 @@ void QUndoStack::push(QUndoCommand *cmd)
         }
     } else {
         if (macro) {
-            d->macro_stack.last()->d->child_list.append(cmd);
+            d->macro_stack.constLast()->d->child_list.append(cmd);
         } else {
             d->command_list.append(cmd);
             d->checkUndoLimit();
@@ -963,7 +963,7 @@ void QUndoStack::beginMacro(const QString &text)
             d->clean_index = -1; // we've deleted the clean state
         d->command_list.append(cmd);
     } else {
-        d->macro_stack.last()->d->child_list.append(cmd);
+        d->macro_stack.constLast()->d->child_list.append(cmd);
     }
     d->macro_stack.append(cmd);