From dff985140a9f31632ba6630ec3391be55051a7ac Mon Sep 17 00:00:00 2001
From: Ivan Solovev <ivan.solovev@qt.io>
Date: Fri, 30 Sep 2022 13:12:42 +0200
Subject: Move qAsConst() and qExchange() to QtTypeTraits

It's the least worst place we could think of.

Add the qttypetraits.h include to qforeach, because otherwise
the tests fail to build.

Task-number: QTBUG-106154
Task-number: QTBUG-99313
Change-Id: I841f22e887f351146589377ec2376957e2adfd5e
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/global/qglobal.cpp | 96 ------------------------------------------
 1 file changed, 96 deletions(-)

(limited to 'src/corelib/global/qglobal.cpp')

diff --git a/src/corelib/global/qglobal.cpp b/src/corelib/global/qglobal.cpp
index 7077efb662..e444755f1b 100644
--- a/src/corelib/global/qglobal.cpp
+++ b/src/corelib/global/qglobal.cpp
@@ -227,102 +227,6 @@ void qAbort()
 // localtime() -- but not localtime_r(), which we use when threaded
 // strftime() -- not used (except in tests)
 
-/*!
-    \fn template <typename T> typename std::add_const<T>::type &qAsConst(T &t)
-    \relates <QtGlobal>
-    \since 5.7
-
-    Returns \a t cast to \c{const T}.
-
-    This function is a Qt implementation of C++17's std::as_const(),
-    a cast function like std::move(). But while std::move() turns
-    lvalues into rvalues, this function turns non-const lvalues into
-    const lvalues. Like std::as_const(), it doesn't work on rvalues,
-    because it cannot be efficiently implemented for rvalues without
-    leaving dangling references.
-
-    Its main use in Qt is to prevent implicitly-shared Qt containers
-    from detaching:
-    \snippet code/src_corelib_global_qglobal.cpp as-const-0
-
-    Of course, in this case, you could (and probably should) have declared
-    \c s as \c const in the first place:
-    \snippet code/src_corelib_global_qglobal.cpp as-const-1
-    but often that is not easily possible.
-
-    It is important to note that qAsConst() does not copy its argument,
-    it just performs a \c{const_cast<const T&>(t)}. This is also the reason
-    why it is designed to fail for rvalues: The returned reference would go
-    stale too soon. So while this works (but detaches the returned object):
-    \snippet code/src_corelib_global_qglobal.cpp as-const-2
-
-    this would not:
-    \snippet code/src_corelib_global_qglobal.cpp as-const-3
-
-    To prevent this construct from compiling (and failing at runtime), qAsConst() has
-    a second, deleted, overload which binds to rvalues.
-*/
-
-/*!
-    \fn template <typename T> void qAsConst(const T &&t)
-    \relates <QtGlobal>
-    \since 5.7
-    \overload
-
-    This overload is deleted to prevent a dangling reference in code like
-    \snippet code/src_corelib_global_qglobal.cpp as-const-4
-*/
-
-/*!
-    \fn template <typename T, typename U = T> T qExchange(T &obj, U &&newValue)
-    \relates <QtGlobal>
-    \since 5.14
-
-    Replaces the value of \a obj with \a newValue and returns the old value of \a obj.
-
-    This is Qt's implementation of std::exchange(). It differs from std::exchange()
-    only in that it is \c constexpr already in C++14, and available on all supported
-    compilers.
-
-    Here is how to use qExchange() to implement move constructors:
-    \code
-    MyClass(MyClass &&other)
-      : m_pointer{qExchange(other.m_pointer, nullptr)},
-        m_int{qExchange(other.m_int, 0)},
-        m_vector{std::move(other.m_vector)},
-        ...
-    \endcode
-
-    For members of class type, we can use std::move(), as their move-constructor will
-    do the right thing. But for scalar types such as raw pointers or integer type, move
-    is the same as copy, which, particularly for pointers, is not what we expect. So, we
-    cannot use std::move() for such types, but we can use std::exchange()/qExchange() to
-    make sure the source object's member is already reset by the time we get to the
-    initialization of our next data member, which might come in handy if the constructor
-    exits with an exception.
-
-    Here is how to use qExchange() to write a loop that consumes the collection it
-    iterates over:
-    \code
-    for (auto &e : qExchange(collection, {})
-        doSomethingWith(e);
-    \endcode
-
-    Which is equivalent to the following, much more verbose code:
-    \code
-    {
-        auto tmp = std::move(collection);
-        collection = {};                    // or collection.clear()
-        for (auto &e : tmp)
-            doSomethingWith(e);
-    }                                       // destroys 'tmp'
-    \endcode
-
-    This is perfectly safe, as the for-loop keeps the result of qExchange() alive for as
-    long as the loop runs, saving the declaration of a temporary variable. Be aware, though,
-    that qExchange() returns a non-const object, so Qt containers may detach.
-*/
-
 /*!
     \macro Q_UNUSED(name)
     \relates <QtGlobal>
-- 
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