bind_front.hpp

#pragma once

// C++20 bind_front
// https://cpprefjp.github.io/reference/functional/bind_front.html
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0356r5.html
#ifndef __cpp_lib_bind_front

#include <utility>
#include <functional>

namespace std {

template <class ...Arg, size_t ...N>
auto _bind_front(std::index_sequence<N...> seq, Arg &&...arg) {
	return std::bind(std::forward<Arg>(arg)..., std::_Placeholder<N + 1>{}...);
}

template <class Class, class Ret, class ...Arg, class ...Bind>
auto bind_front(Ret(Class::*func)(Arg...) const, Bind &&...bind) {
	auto seq = std::make_index_sequence<sizeof...(Arg) - sizeof...(Bind) + 1>();
	return _bind_front(seq, func, std::forward<Bind>(bind)...);
}

template <class Class, class Ret, class ...Arg, class ...Bind>
auto bind_front(Ret(Class::*func)(Arg...), Bind &&...bind) {
	auto seq = std::make_index_sequence<sizeof...(Arg) - sizeof...(Bind) + 1>();
	return _bind_front(seq, func, std::forward<Bind>(bind)...);
}

template <class Ret, class ...Arg, class ...Bind>
auto bind_front(Ret(*func)(Arg...), Bind &&...bind) {
	auto seq = std::make_index_sequence<sizeof...(Arg) - sizeof...(Bind)>();
	return _bind_front(seq, func, std::forward<Bind>(bind)...);
}

template <class Ret, class ...Arg, class ...Bind>
auto bind_front(std::function<Ret(Arg...)> &func, Bind &&...bind) {
	auto seq = std::make_index_sequence<sizeof...(Arg) - sizeof...(Bind)>();
	return _bind_front(seq, func, std::forward<Bind>(bind)...);
}

template <class Ret, class ...Arg, class ...Bind>
auto bind_front(std::function<Ret(Arg...)> &&func, Bind &&...bind) {
	auto seq = std::make_index_sequence<sizeof...(Arg) - sizeof...(Bind)>();
	return _bind_front(seq, std::move(func), std::forward<Bind>(bind)...);
}

} // namespace std

#endif // __cpp_lib_bind_front