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Fix deep-const-correctness of qGetPtrHelper() for smart pointers

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The function qGetPtrHelper() is mainly used to implement d_func() within
the Q_DECLARE_PRIVATE() macro. The whole purpose of d_func() is to
propagate const deeply. But if a smart pointer implements this by itself,
then the old version of qGetPtrHelper(), by taking the Ptr as a const-&,
would always return a const payload pointer, which would fail in the
following reinterpret_cast in d_func() to mutable payloads.

This was found while experimenting with making QExplicitlySharedDataPointer
deep const-correct, and I have no explanation why it seems to have worked
with QSharedDataPointer, which is deep-const-correct already.

Change-Id: Iee2e8fcce89c58ba2af7818de6f79ed39c5a4030
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Marc Mutz 2019-06-13 23:25:18 +02:00
parent 079dafc42f
commit f2bd46d1df
1 changed files with 1 additions and 1 deletions
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2
src/corelib/global/qglobal.h
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@ -1096,7 +1096,7 @@ for (auto _container_ = QtPrivate::qMakeForeachContainer(container); \
#endif
template <typename T> inline T *qGetPtrHelper(T *ptr) { return ptr; }
template <typename Ptr> inline auto qGetPtrHelper(const Ptr &ptr) -> decltype(ptr.operator->()) { return ptr.operator->(); }
template <typename Ptr> inline auto qGetPtrHelper(Ptr &ptr) -> decltype(ptr.operator->()) { return ptr.operator->(); }
// The body must be a statement:
#define Q_CAST_IGNORE_ALIGN(body) QT_WARNING_PUSH QT_WARNING_DISABLE_GCC("-Wcast-align") body QT_WARNING_POP