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+/*!
+@file
+Defines `boost::hana::Constant`.
+
+@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_CONCEPT_CONSTANT_HPP
+#define BOOST_HANA_CONCEPT_CONSTANT_HPP
+
+#include <boost/hana/fwd/concept/constant.hpp>
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/default.hpp>
+#include <boost/hana/core/tag_of.hpp>
+#include <boost/hana/value.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+ template <typename C>
+ struct Constant {
+ using Tag = typename tag_of<C>::type;
+ static constexpr bool value = !is_default<value_impl<Tag>>::value;
+ };
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_CONCEPT_CONSTANT_HPP