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Warn if Q_FOREACH is used with a non-shared container

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Show a deprecation warning if a non shared container is used within
Q_FOREACH, because it would make an expensive copy of the container

Change-Id: I70cfd789b5b8d9f5b1bd6e0a57e5e968e1c6a0ca
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
This commit is contained in:
Olivier Goffart 2018-10-29 14:33:27 +01:00 committed by Giuseppe D'Angelo
parent d76b9d86e8
commit 1926e09b32
1 changed files with 14 additions and 0 deletions
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14
src/corelib/global/qglobal.h
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@ -1083,9 +1083,23 @@ public:
int control = 1; int control = 1;
}; };
// Containers that have a detach function are considered shared, and are OK in a foreach loop
template <typename T, typename = decltype(std::declval<T>().detach())>
inline void warnIfContainerIsNotShared(int) {}
#if QT_DEPRECATED_SINCE(6, 0)
// Other containers will copy themselves if used in foreach, this use is deprecated
template <typename T>
QT_DEPRECATED_VERSION_X_6_0("Do not use foreach/Q_FOREACH with containers which are not implicitly shared. "
"Prefer using a range-based for loop with these containers: `for (const auto &it : container)`, "
"keeping in mind that range-based for doesn't copy the container as Q_FOREACH does")
inline void warnIfContainerIsNotShared(...) {}
#endif
template<typename T> template<typename T>
QForeachContainer<typename std::decay<T>::type> qMakeForeachContainer(T &&t) QForeachContainer<typename std::decay<T>::type> qMakeForeachContainer(T &&t)
{ {
warnIfContainerIsNotShared<typename std::decay<T>::type>(0);
return QForeachContainer<typename std::decay<T>::type>(std::forward<T>(t)); return QForeachContainer<typename std::decay<T>::type>(std::forward<T>(t));
} }