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Diffstat (limited to 'src/corelib/global/q23utility.h')
-rw-r--r-- | src/corelib/global/q23utility.h | 75 |
1 files changed, 75 insertions, 0 deletions
diff --git a/src/corelib/global/q23utility.h b/src/corelib/global/q23utility.h new file mode 100644 index 0000000000..9ae5389b56 --- /dev/null +++ b/src/corelib/global/q23utility.h @@ -0,0 +1,75 @@ +// Copyright (C) 2023 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 Q23UTILITY_H +#define Q23UTILITY_H + +#include <QtCore/qtconfigmacros.h> + +#include <utility> + +// +// W A R N I N G +// ------------- +// +// This file is not part of the Qt API. Types and functions defined in this +// file can reliably be replaced by their std counterparts, once available. +// You may use these definitions in your own code, but be aware that we +// will remove them once Qt depends on the C++ version that supports +// them in namespace std. There will be NO deprecation warning, the +// definitions will JUST go away. +// +// If you can't agree to these terms, don't use these definitions! +// +// We mean it. +// + +QT_BEGIN_NAMESPACE + +namespace q23 { +// like std::forward_like +#ifdef __cpp_lib_forward_like +using std::forward_like; +#else + +namespace _detail { + +// [forward]/6.1 COPY_CONST +template <typename A, typename B> +using copy_const_t = std::conditional_t< + std::is_const_v<A>, const B, + /* else */ B + >; + +// [forward]/6.2 OVERRIDE_REF +template <typename A, typename B> +using override_ref_t = std::conditional_t< + std::is_rvalue_reference_v<A>, std::remove_reference_t<B>&&, + /* else */ B& + >; + +// [forward]/6.3 "V" +template <typename T, typename U> +using forward_like_ret_t = override_ref_t< + T&&, + copy_const_t< + std::remove_reference_t<T>, + std::remove_reference_t<U> + > + >; + +} // namespace detail + +// http://eel.is/c++draft/forward#lib:forward_like +template <class T, class U> +[[nodiscard]] constexpr auto forward_like(U &&x) noexcept + -> _detail::forward_like_ret_t<T, U> +{ + using V = _detail::forward_like_ret_t<T, U>; + return static_cast<V>(x); +} +#endif // __cpp_lib_forward_like +} // namespace q23 + +QT_END_NAMESPACE + +#endif /* Q23UTILITY_H */ |