39 lines
943 B
C++
39 lines
943 B
C++
/*!
|
|
@file
|
|
Defines `boost::hana::id`.
|
|
|
|
@copyright Louis Dionne 2013-2016
|
|
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_ID_HPP
|
|
#define BOOST_HANA_FUNCTIONAL_ID_HPP
|
|
|
|
#include <boost/hana/config.hpp>
|
|
|
|
|
|
BOOST_HANA_NAMESPACE_BEGIN
|
|
//! @ingroup group-functional
|
|
//! The identity function -- returns its argument unchanged.
|
|
//!
|
|
//! ### Example
|
|
//! @include example/functional/id.cpp
|
|
#ifdef BOOST_HANA_DOXYGEN_INVOKED
|
|
constexpr auto id = [](auto&& x) -> decltype(auto) {
|
|
return forwarded(x);
|
|
};
|
|
#else
|
|
struct id_t {
|
|
template <typename T>
|
|
constexpr T operator()(T&& t) const {
|
|
return static_cast<T&&>(t);
|
|
}
|
|
};
|
|
|
|
constexpr id_t id{};
|
|
#endif
|
|
BOOST_HANA_NAMESPACE_END
|
|
|
|
#endif // !BOOST_HANA_FUNCTIONAL_ID_HPP
|