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+/*!
+@file
+Defines `boost::hana::always`.
+
+@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_FUNCTIONAL_ALWAYS_HPP
+#define BOOST_HANA_FUNCTIONAL_ALWAYS_HPP
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/detail/create.hpp>
+
+#include <utility>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! @ingroup group-functional
+    //! Return a constant function returning `x` regardless of the
+    //! argument(s) it is invoked with.
+    //!
+    //! Specifically, `always(x)` is a function such that
+    //! @code
+    //!     always(x)(y...) == x
+    //! @endcode
+    //! for any `y...`. A copy of `x` is made and it is owned by the
+    //! `always(x)` function. When `always(x)` is called, it will return
+    //! a reference to the `x` it owns. This reference is valid as long
+    //! as `always(x)` is in scope.
+    //!
+    //!
+    //! ### Example
+    //! @include example/functional/always.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    constexpr auto always = [](auto&& x) {
+        return [perfect-capture](auto const& ...y) -> decltype(auto) {
+            return forwarded(x);
+        };
+    };
+#else
+    template <typename T>
+    struct _always {
+        T val_;
+
+        template <typename ...Args>
+        constexpr T const& operator()(Args const& ...) const&
+        { return val_; }
+
+        template <typename ...Args>
+        constexpr T& operator()(Args const& ...) &
+        { return val_; }
+
+        template <typename ...Args>
+        constexpr T operator()(Args const& ...) &&
+        { return std::move(val_); }
+    };
+
+    constexpr detail::create<_always> always{};
+#endif
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FUNCTIONAL_ALWAYS_HPP