bind_front.hpp

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// SPDX-License-Identifier: BSL-1.0
// SPDX-FileCopyrightText: Copyright (C) 2021 Tobias Hienzsch
 
#ifndef TETL_FUNCTIONAL_BIND_FRONT_HPP
#define TETL_FUNCTIONAL_BIND_FRONT_HPP
 
#include <etl/_functional/invoke.hpp>
#include <etl/_tuple/apply.hpp>
#include <etl/_tuple/tuple.hpp>
#include <etl/_type_traits/decay.hpp>
#include <etl/_type_traits/invoke_result.hpp>
#include <etl/_type_traits/is_base_of.hpp>
#include <etl/_type_traits/unwrap_reference.hpp>
#include <etl/_utility/forward.hpp>
#include <etl/_utility/move.hpp>
 
namespace etl {
 
namespace detail {
 
template <typename Func, typename BoundArgsTuple, typename... CallArgs>
constexpr auto bind_front_caller(Func&& func, BoundArgsTuple&& boundArgsTuple, CallArgs&&... callArgs) -> decltype(auto)
{
    return etl::apply([&func, &callArgs...]<typename... BoundArgs>(BoundArgs&&... boundArgs) -> decltype(auto) {
        return etl::invoke(
            etl::forward<Func>(func),
            etl::forward<BoundArgs>(boundArgs)...,
            etl::forward<CallArgs>(callArgs)...
        );
    }, etl::forward<BoundArgsTuple>(boundArgsTuple));
}
 
template <typename Func, typename... BoundArgs>
class bind_front_t {
public:
    template <typename F, typename... BA>
        requires(!(sizeof...(BA) == 0 && is_base_of_v<bind_front_t, decay_t<F>>))
    explicit bind_front_t(F&& f, BA&&... ba)
        : _func(etl::forward<F>(f))
        , _boundArgs(etl::forward<BA>(ba)...)
    {
    }
 
    // TODO: Add noexcept(is_nothrow_invocable_v<Func&, BoundArgs&..., CallArgs...>)
    template <typename... CallArgs>
    auto operator()(CallArgs&&... callArgs) & -> invoke_result_t<Func&, BoundArgs&..., CallArgs...>
    {
        return bind_front_caller(_func, _boundArgs, etl::forward<CallArgs>(callArgs)...);
    }
 
    // TODO: Add noexcept(is_nothrow_invocable_v<Func const&, BoundArgs const&...,CallArgs...>)
    template <typename... CallArgs>
    auto operator()(CallArgs&&... callArgs) const& -> invoke_result_t<Func const&, BoundArgs const&..., CallArgs...>
    {
        return bind_front_caller(_func, _boundArgs, etl::forward<CallArgs>(callArgs)...);
    }
 
    // TODO: Add  noexcept(is_nothrow_invocable_v<Func, BoundArgs..., CallArgs...>)
    template <typename... CallArgs>
    auto operator()(CallArgs&&... callArgs) && -> invoke_result_t<Func, BoundArgs..., CallArgs...>
    {
        return bind_front_caller(etl::move(_func), etl::move(_boundArgs), etl::forward<CallArgs>(callArgs)...);
    }
 
    // TODO: noexcept(is_nothrow_invocable_v<Func const, BoundArgs const...,CallArgs...>)
    template <typename... CallArgs>
    auto operator()(CallArgs&&... callArgs) const&& -> invoke_result_t<Func const, BoundArgs const..., CallArgs...>
    {
        return bind_front_caller(etl::move(_func), etl::move(_boundArgs), etl::forward<CallArgs>(callArgs)...);
    }
 
private:
    Func _func;
    tuple<BoundArgs...> _boundArgs;
};
 
} // namespace detail
 
/// \brief The function template bind_front generates a forwarding call wrapper
/// for f. Calling this wrapper is equivalent to invoking f with its first
/// sizeof...(Args) parameters bound to args. In other words, bind_front(f,
/// bound_args...)(call_args...) is equivalent to invoke(f, bound_args...,
/// call_args....).
///
/// \details Copied implementation from paper:
/// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0356r5.html
template <typename Func, typename... BoundArgs>
constexpr auto bind_front(Func&& func, BoundArgs&&... boundArgs)
{
    return detail::bind_front_t<decay_t<Func>, unwrap_ref_decay_t<BoundArgs>...>{
        etl::forward<Func>(func),
        etl::forward<BoundArgs>(boundArgs)...
    };
}
 
} // namespace etl
 
#endif // TETL_FUNCTIONAL_BIND_FRONT_HPP