QList: improve the range constructors

In case of forward iterators, call std::distance just once and not
twice. In case of non-forward iterators, don't call
reserveIfForwardIterator -- as the name says, it doesn't make sense
on non-forward iterators.

Change-Id: I7e6a603205286c05f7bc7c47fd1f1e0d92705b20
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 4 insertions, 4 deletions

diff --git a/src/corelib/tools/qlist.h b/src/corelib/tools/qlist.h
index e041b4132a..5d0a95fb0b 100644
--- a/src/corelib/tools/qlist.h
+++ b/src/corelib/tools/qlist.h
@@ -144,17 +144,17 @@ public:
     }
     template <typename InputIterator, QtPrivate::IfIsForwardIterator<InputIterator> = true>
     QList(InputIterator i1, InputIterator i2)
-        : d(Data::allocate(std::distance(i1, i2)))
     {
-        if (std::distance(i1, i2))
+        const auto distance = std::distance(i1, i2);
+        if (distance) {
+            d = DataPointer(Data::allocate(distance));
             d->copyAppend(i1, i2);
+        }
     }
 
     template <typename InputIterator, QtPrivate::IfIsNotForwardIterator<InputIterator> = true>
     QList(InputIterator i1, InputIterator i2)
-        : QList()
     {
-        QtPrivate::reserveIfForwardIterator(this, i1, i2);
         std::copy(i1, i2, std::back_inserter(*this));
     }