include/QtCore/qforeach.h

0001 // Copyright (C) 2022 The Qt Company Ltd.
0002 // Copyright (C) 2019 Intel Corporation.
0003 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
0004
0005 #ifndef QFOREACH_H
0006 #define QFOREACH_H
0007
0008 #include <QtCore/qtclasshelpermacros.h>
0009 #include <QtCore/qtconfigmacros.h>
0010 #include <QtCore/qtdeprecationmarkers.h>
0011 #include <QtCore/qttypetraits.h>
0012
0013 QT_BEGIN_NAMESPACE
0014
0015 #if 0
0016 #pragma qt_class(QForeach)
0017 #pragma qt_sync_stop_processing
0018 #endif
0019
0020 #ifndef QT_NO_FOREACH
0021
0022 namespace QtPrivate {
0023
0024 template <typename T>
0025 class QForeachContainer {
0026     Q_DISABLE_COPY_MOVE(QForeachContainer)
0027 public:
0028     QForeachContainer(const T &t) : c(t), i(std::as_const(c).begin()), e(std::as_const(c).end()) {}
0029     QForeachContainer(T &&t) : c(std::move(t)), i(std::as_const(c).begin()), e(std::as_const(c).end())  {}
0030
0031     T c;
0032     typename T::const_iterator i, e;
0033 };
0034
0035 // Containers that have a detach function are considered shared, and are OK in a foreach loop
0036 template <typename T, typename = decltype(std::declval<T>().detach())>
0037 inline void warnIfContainerIsNotShared(int) {}
0038
0039 #if QT_DEPRECATED_SINCE(6, 0)
0040 // Other containers will copy themselves if used in foreach, this use is deprecated
0041 template <typename T>
0042 QT_DEPRECATED_VERSION_X_6_0("Do not use foreach/Q_FOREACH with containers which are not implicitly shared. "
0043     "Prefer using a range-based for loop with these containers: `for (const auto &it : container)`, "
0044     "keeping in mind that range-based for doesn't copy the container as Q_FOREACH does")
0045 inline void warnIfContainerIsNotShared(...) {}
0046 #endif
0047
0048 template<typename T>
0049 QForeachContainer<typename std::decay<T>::type> qMakeForeachContainer(T &&t)
0050 {
0051     warnIfContainerIsNotShared<typename std::decay<T>::type>(0);
0052     return QForeachContainer<typename std::decay<T>::type>(std::forward<T>(t));
0053 }
0054
0055 }
0056
0057 // Use C++17 if statement with initializer. User's code ends up in a else so
0058 // scoping of different ifs is not broken
0059 #define Q_FOREACH_IMPL(variable, name, container)                                             \
0060     for (auto name = QtPrivate::qMakeForeachContainer(container); name.i != name.e; ++name.i) \
0061         if (variable = *name.i; false) {} else
0062
0063 #define Q_FOREACH_JOIN(A, B) Q_FOREACH_JOIN_IMPL(A, B)
0064 #define Q_FOREACH_JOIN_IMPL(A, B) A ## B
0065
0066 #define Q_FOREACH(variable, container) \
0067     Q_FOREACH_IMPL(variable, Q_FOREACH_JOIN(_container_, __LINE__), container)
0068 #endif // QT_NO_FOREACH
0069
0070 #define Q_FOREVER for(;;)
0071 #ifndef QT_NO_KEYWORDS
0072 # ifndef QT_NO_FOREACH
0073 #  ifndef foreach
0074 #    define foreach Q_FOREACH
0075 #  endif
0076 # endif // QT_NO_FOREACH
0077 #  ifndef forever
0078 #    define forever Q_FOREVER
0079 #  endif
0080 #endif
0081
0082 QT_END_NAMESPACE
0083
0084 #endif /* QFOREACH_H */