callback-converter.h

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// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Author: PBS <pbs3141@gmail.com>
 * Copyright (C) 2022 Authors
 * Released under GNU GPL v2+, read the file 'COPYING' for more information.
 */
#ifndef INKSCAPE_UTIL_CALLBACK_CONVERTER_H
#define INKSCAPE_UTIL_CALLBACK_CONVERTER_H
 
#include <utility>
 
namespace Inkscape::Util {
namespace detail {
 
template <auto Fp>
struct CallbackConverter
{
    template <typename T>
    struct Helper;
 
    template <typename Ret, typename Obj, typename... Args>
    struct Helper<Ret(Obj::*)(Args...)>
    {
        // Unary plus converts lambda to function pointer.
        static constexpr auto result = +[] (Args... args, void *data) -> Ret {
            return (reinterpret_cast<Obj*>(data)->*Fp)(std::forward<Args>(args)...);
        };
    };
 
    static constexpr auto result = Helper<decltype(Fp)>::result;
};
 
} // namespace detail
 
template <auto Fp>
constexpr auto make_c_callback = detail::CallbackConverter<Fp>::result;
 
template <auto Fp>
inline auto make_g_callback = reinterpret_cast<void(*)()>(make_c_callback<Fp>); // inline instead of constexpr due to reinterpret_cast
 
} // namespace Inkscape::Util
 
#endif // INKSCAPE_UTIL_CALLBACK_CONVERTER_H