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 Hu Chunming
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/*!
@file
Defines `boost::hana::apply`.
Copyright Louis Dionne 2013-2022
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
*/
#ifndef BOOST_HANA_FUNCTIONAL_APPLY_HPP
#define BOOST_HANA_FUNCTIONAL_APPLY_HPP
#include <boost/hana/config.hpp>
namespace boost { namespace hana {
//! @ingroup group-functional
//! Invokes a Callable with the given arguments.
//!
//! This is equivalent to [std::invoke][1] that will be added in C++17.
//! However, `apply` is a function object instead of a function, which
//! makes it possible to pass it to higher-order algorithms.
//!
//!
//! @param f
//! A [Callable][2] to be invoked with the given arguments.
//!
//! @param x...
//! The arguments to call `f` with. The number of `x...` must match the
//! arity of `f`.
//!
//!
//! Example
//! -------
//! @include example/functional/apply.cpp
//!
//! [1]: http://en.cppreference.com/w/cpp/utility/functional/invoke
//! [2]: http://en.cppreference.com/w/cpp/named_req/Callable
#ifdef BOOST_HANA_DOXYGEN_INVOKED
constexpr auto apply = [](auto&& f, auto&& ...x) -> decltype(auto) {
return forwarded(f)(forwarded(x)...);
};
#else
struct apply_t {
template <typename F, typename... Args>
constexpr auto operator()(F&& f, Args&&... args) const ->
decltype(static_cast<F&&>(f)(static_cast<Args&&>(args)...))
{
return static_cast<F&&>(f)(static_cast<Args&&>(args)...);
}
template <typename Base, typename T, typename Derived>
constexpr auto operator()(T Base::*pmd, Derived&& ref) const ->
decltype(static_cast<Derived&&>(ref).*pmd)
{
return static_cast<Derived&&>(ref).*pmd;
}
template <typename PMD, typename Pointer>
constexpr auto operator()(PMD pmd, Pointer&& ptr) const ->
decltype((*static_cast<Pointer&&>(ptr)).*pmd)
{
return (*static_cast<Pointer&&>(ptr)).*pmd;
}
template <typename Base, typename T, typename Derived, typename... Args>
constexpr auto operator()(T Base::*pmf, Derived&& ref, Args&&... args) const ->
decltype((static_cast<Derived&&>(ref).*pmf)(static_cast<Args&&>(args)...))
{
return (static_cast<Derived&&>(ref).*pmf)(static_cast<Args&&>(args)...);
}
template <typename PMF, typename Pointer, typename... Args>
constexpr auto operator()(PMF pmf, Pointer&& ptr, Args&& ...args) const ->
decltype(((*static_cast<Pointer&&>(ptr)).*pmf)(static_cast<Args&&>(args)...))
{
return ((*static_cast<Pointer&&>(ptr)).*pmf)(static_cast<Args&&>(args)...);
}
};
BOOST_HANA_INLINE_VARIABLE constexpr apply_t apply{};
#endif
}} // end namespace boost::hana
#endif // !BOOST_HANA_FUNCTIONAL_APPLY_HPP
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