qttypetraits.h

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// Copyright (C) 2022 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
#ifndef QTTYPETRAITS_H
#define QTTYPETRAITS_H
 
#include <QtCore/qtconfigmacros.h>
#include <QtCore/qtdeprecationmarkers.h>
 
#include <type_traits>
#include <utility>
 
#if 0
#pragma qt_class(QtTypeTraits)
#pragma qt_sync_stop_processing
#endif
 
QT_BEGIN_NAMESPACE
 
// like std::is_constant_evaluated
#define QT_SUPPORTS_IS_CONSTANT_EVALUATED
#ifdef __cpp_lib_is_constant_evaluated
constexpr bool qIsConstantEvaluated() noexcept
{
    return std::is_constant_evaluated();
}
#elif __has_builtin(__builtin_is_constant_evaluated) || \
    (defined(Q_CC_MSVC_ONLY) /* >= 1925, but we require 1927 in qglobal.h */)
constexpr bool qIsConstantEvaluated() noexcept
{
    return __builtin_is_constant_evaluated();
}
#else
#  undef QT_SUPPORTS_IS_CONSTANT_EVALUATED
#endif
 
// like std::to_underlying
template <typename Enum>
constexpr std::underlying_type_t<Enum> qToUnderlying(Enum e) noexcept
{
    return static_cast<std::underlying_type_t<Enum>>(e);
}
 
#ifndef QT_NO_AS_CONST
#if QT_DEPRECATED_SINCE(6, 6)
 
// this adds const to non-const objects (like std::as_const)
template <typename T>
QT_DEPRECATED_VERSION_X_6_6("Use std::as_const() instead.")
constexpr typename std::add_const<T>::type &qAsConst(T &t) noexcept { return t; }
// prevent rvalue arguments:
template <typename T>
void qAsConst(const T &&) = delete;
 
#endif // QT_DEPRECATED_SINCE(6, 6)
#endif // QT_NO_AS_CONST
 
#ifndef QT_NO_QEXCHANGE
 
// like std::exchange
template <typename T, typename U = T>
constexpr T qExchange(T &t, U &&newValue)
noexcept(std::conjunction_v<std::is_nothrow_move_constructible<T>,
                            std::is_nothrow_assignable<T &, U>>)
{
    T old = std::move(t);
    t = std::forward<U>(newValue);
    return old;
}
 
#endif // QT_NO_QEXCHANGE
 
namespace QtPrivate {
// helper to be used to trigger a "dependent static_assert(false)"
// (for instance, in a final `else` branch of a `if constexpr`.)
template <typename T> struct type_dependent_false : std::false_type {};
template <auto T> struct value_dependent_false : std::false_type {};
}
 
QT_END_NAMESPACE
 
#endif // QTTYPETRAITS_H