/*!
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@file
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Forward declares `boost::hana::is_a` and `boost::hana::is_an`.
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@copyright Louis Dionne 2013-2017
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_FWD_CORE_IS_A_HPP
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#define BOOST_HANA_FWD_CORE_IS_A_HPP
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#include <boost/hana/config.hpp>
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BOOST_HANA_NAMESPACE_BEGIN
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//! @ingroup group-core
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//! Returns whether the tag of an object matches a given tag.
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//!
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//! Given a tag `Tag` and a C++ type `T`, `is_a<Tag, T>` is a compile-time
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//! Logical representing whether the tag of `T` is exactly `Tag`. In other
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//! words, it is equivalent to
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//! @code
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//! std::is_same<Tag, tag_of<T>::type>
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//! @endcode
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//!
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//! For convenience, an alternate syntax is provided for using `is_a`.
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//! Specifically, `is_a<Tag>` is a function object returning whether the
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//! argument it is passed has the given tag. In other words,
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//! @code
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//! is_a<Tag>(x) == is_a<Tag, decltype(x)>
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//! @endcode
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//!
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//!
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//! Example
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//! -------
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//! @include example/core/is_a.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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template <typename Tag, typename optional_T>
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constexpr auto is_a = see-documentation;
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#else
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template <typename Tag, typename ...T>
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struct is_a_t;
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template <typename Tag, typename ...T>
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constexpr is_a_t<Tag, T...> is_a{};
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#endif
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//! @ingroup group-core
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//! Equivalent to `is_a`; provided for consistency with the rules of the
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//! English language.
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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template <typename Tag, typename ...T>
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constexpr auto is_an = is_a<Tag, T...>;
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#else
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template <typename Tag, typename ...T>
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constexpr is_a_t<Tag, T...> is_an{};
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#endif
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FWD_CORE_IS_A_HPP
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