feat():initial version

install/boost_1_75_0/include/boost/hof/decay.hpp

@@ -0,0 +1,68 @@
+/*=============================================================================
+    Copyright (c) 2015 Paul Fultz II
+    decay.h
+    Distributed under the Boost Software License, Version 1.0. (See accompanying
+    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+==============================================================================*/
+
+#ifndef BOOST_HOF_GUARD_DECAY_H
+#define BOOST_HOF_GUARD_DECAY_H
+
+/// decay
+/// =====
+/// 
+/// Description
+/// -----------
+/// 
+/// The `decay` function is a unary function object that returns whats given to it after decaying its type.
+/// 
+/// Synopsis
+/// --------
+/// 
+///     struct
+///     {
+///         template<class T>
+///         constexpr typename decay<T>::type operator()(T&& x) const
+///         {
+///             return boost::hof::forward<T>(x);
+///         }
+///     } decay;
+/// 
+/// References
+/// ----------
+/// 
+/// * [n3255](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3255.html) - Proposal for `decay_copy`
+/// 
+
+#include <boost/hof/detail/delegate.hpp>
+#include <boost/hof/detail/unwrap.hpp>
+#include <boost/hof/detail/static_const_var.hpp>
+#include <boost/hof/detail/forward.hpp>
+
+namespace boost { namespace hof { namespace detail {
+
+template<class T>
+struct decay_mf
+: unwrap_reference<typename std::decay<T>::type>
+{};
+
+struct decay_f
+{
+    template<
+        class T, 
+        class Result=typename unwrap_reference<typename std::decay<T>::type>::type, 
+        class=typename std::enable_if<(BOOST_HOF_IS_CONSTRUCTIBLE(Result, T))>::type
+    >
+    constexpr Result operator()(T&& x) const BOOST_HOF_NOEXCEPT_CONSTRUCTIBLE(Result, T&&)
+    {
+        return BOOST_HOF_FORWARD(T)(x);
+    }
+};
+
+}
+
+BOOST_HOF_DECLARE_STATIC_VAR(decay, detail::decay_f);
+
+}} // namespace boost::hof
+
+#endif