1/*!
2@file
3Forward declares `boost::hana::make`.
4
5Copyright Louis Dionne 2013-2022
6Distributed under the Boost Software License, Version 1.0.
7(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
8 */
9
10#ifndef BOOST_HANA_FWD_CORE_MAKE_HPP
11#define BOOST_HANA_FWD_CORE_MAKE_HPP
12
13#include <boost/hana/config.hpp>
14
15
16namespace boost { namespace hana {
17 //! @ingroup group-core
18 //! Create an object of the given tag with the given arguments.
19 //!
20 //! This function serves the same purpose as constructors in usual C++.
21 //! However, instead of creating an object of a specific C++ type, it
22 //! creates an object of a specific tag, regardless of the C++ type
23 //! of that object.
24 //!
25 //! This function is actually a variable template, so `make<T>` can be
26 //! passed around as a function object creating an object of tag `T`.
27 //! Also, it uses tag-dispatching so this is how it should be customized
28 //! for user-defined tags.
29 //!
30 //! Finally, the default implementation of `make` is equivalent to calling
31 //! the constructor of the given tag with the corresponding arguments.
32 //! In other words, by default,
33 //! @code
34 //! make<T>(args...) == T(args...)
35 //! @endcode
36 //!
37 //! Note that the arguments are perfectly forwarded and the form of
38 //! construction which is used is exactly as documented, i.e. `T(args...)`.
39 //! However, if `T(args...)` is not a valid expression, a compilation
40 //! error is triggered. This default behavior is useful because it makes
41 //! foreign C++ types that have no notion of tag constructible with `make`
42 //! out-of-the-box, since their tag is exactly themselves.
43 //!
44 //!
45 //! Example
46 //! -------
47 //! @include example/core/make.cpp
48#ifdef BOOST_HANA_DOXYGEN_INVOKED
49 template <typename Tag>
50 constexpr auto make = [](auto&& ...x) -> decltype(auto) {
51 return tag-dispatched;
52 };
53#else
54 template <typename Tag, typename = void>
55 struct make_impl;
56
57 template <typename Tag>
58 struct make_t {
59 template <typename ...X>
60 constexpr decltype(auto) operator()(X&& ...x) const {
61 return make_impl<Tag>::apply(static_cast<X&&>(x)...);
62 }
63 };
64
65 template <typename Tag>
66 BOOST_HANA_INLINE_VARIABLE constexpr make_t<Tag> make{};
67#endif
68}} // end namespace boost::hana
69
70#endif // !BOOST_HANA_FWD_CORE_MAKE_HPP
71

source code of boost/libs/hana/include/boost/hana/fwd/core/make.hpp