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/*!
@file
Forward declares `boost::hana::make`.
@copyright Louis Dionne 2013-2017
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_FWD_CORE_MAKE_HPP
#define BOOST_HANA_FWD_CORE_MAKE_HPP
#include <boost/hana/config.hpp>
BOOST_HANA_NAMESPACE_BEGIN
//! @ingroup group-core
//! Create an object of the given tag with the given arguments.
//!
//! This function serves the same purpose as constructors in usual C++.
//! However, instead of creating an object of a specific C++ type, it
//! creates an object of a specific tag, regardless of the C++ type
//! of that object.
//!
//! This function is actually a variable template, so `make<T>` can be
//! passed around as a function object creating an object of tag `T`.
//! Also, it uses tag-dispatching so this is how it should be customized
//! for user-defined tags.
//!
//! Finally, the default implementation of `make` is equivalent to calling
//! the constructor of the given tag with the corresponding arguments.
//! In other words, by default,
//! @code
//! make<T>(args...) == T(args...)
//! @endcode
//!
//! Note that the arguments are perfectly forwarded and the form of
//! construction which is used is exactly as documented, i.e. `T(args...)`.
//! However, if `T(args...)` is not a valid expression, a compilation
//! error is triggered. This default behavior is useful because it makes
//! foreign C++ types that have no notion of tag constructible with `make`
//! out-of-the-box, since their tag is exactly themselves.
//!
//!
//! Example
//! -------
//! @include example/core/make.cpp
#ifdef BOOST_HANA_DOXYGEN_INVOKED
template <typename Tag>
constexpr auto make = [](auto&& ...x) -> decltype(auto) {
return tag-dispatched;
};
#else
template <typename Tag, typename = void>
struct make_impl;
template <typename Tag>
struct make_t {
template <typename ...X>
constexpr decltype(auto) operator()(X&& ...x) const {
return make_impl<Tag>::apply(static_cast<X&&>(x)...);
}
};
template <typename Tag>
constexpr make_t<Tag> make{};
#endif
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_FWD_CORE_MAKE_HPP
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