1/*!
2@file
3Forward declares `boost::hana::is_a` and `boost::hana::is_an`.
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_IS_A_HPP
11#define BOOST_HANA_FWD_CORE_IS_A_HPP
12
13#include <boost/hana/config.hpp>
14
15
16namespace boost { namespace hana {
17 //! @ingroup group-core
18 //! Returns whether the tag of an object matches a given tag.
19 //!
20 //! Given a tag `Tag` and a C++ type `T`, `is_a<Tag, T>` is a compile-time
21 //! Logical representing whether the tag of `T` is exactly `Tag`. In other
22 //! words, it is equivalent to
23 //! @code
24 //! std::is_same<Tag, tag_of<T>::type>
25 //! @endcode
26 //!
27 //! For convenience, an alternate syntax is provided for using `is_a`.
28 //! Specifically, `is_a<Tag>` is a function object returning whether the
29 //! argument it is passed has the given tag. In other words,
30 //! @code
31 //! is_a<Tag>(x) == is_a<Tag, decltype(x)>
32 //! @endcode
33 //!
34 //!
35 //! Example
36 //! -------
37 //! @include example/core/is_a.cpp
38#ifdef BOOST_HANA_DOXYGEN_INVOKED
39 template <typename Tag, typename optional_T>
40 constexpr auto is_a = see-documentation;
41#else
42 template <typename Tag, typename ...T>
43 struct is_a_t;
44
45 template <typename Tag, typename ...T>
46 BOOST_HANA_INLINE_VARIABLE constexpr is_a_t<Tag, T...> is_a{};
47#endif
48
49 //! @ingroup group-core
50 //! Equivalent to `is_a`; provided for consistency with the rules of the
51 //! English language.
52#ifdef BOOST_HANA_DOXYGEN_INVOKED
53 template <typename Tag, typename ...T>
54 constexpr auto is_an = is_a<Tag, T...>;
55#else
56 template <typename Tag, typename ...T>
57 BOOST_HANA_INLINE_VARIABLE constexpr is_a_t<Tag, T...> is_an{};
58#endif
59}} // end namespace boost::hana
60
61#endif // !BOOST_HANA_FWD_CORE_IS_A_HPP
62

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