feat():initial version

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

@@ -0,0 +1,135 @@
+/*=============================================================================
+    Copyright (c) 2014 Paul Fultz II
+    result.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_RESULT_H
+#define BOOST_HOF_GUARD_RESULT_H
+
+/// result
+/// ======
+/// 
+/// Description
+/// -----------
+/// 
+/// The `result` function adaptor sets the return type for the function, which
+/// can be useful when dealing with multiple overloads. Since the return type
+/// is no longer dependent on the parameters passed to the function, the
+/// `result_adaptor` provides a nested `result_type` that is the return type
+/// of the function.
+/// 
+/// Synopsis
+/// --------
+/// 
+///     template<class Result, class F>
+///     constexpr result_adaptor<Result, F> result(F f);
+/// 
+/// Requirements
+/// ------------
+/// 
+/// F must be:
+/// 
+/// * [ConstInvocable](ConstInvocable)
+/// * MoveConstructible
+/// 
+/// Example
+/// -------
+/// 
+///     #include <boost/hof.hpp>
+///     #include <cassert>
+/// 
+///     struct id
+///     {
+///         template<class T>
+///         T operator()(T x) const
+///         {
+///             return x;
+///         }
+///     };
+/// 
+///     int main() {
+///         auto int_result = boost::hof::result<int>(id());
+///         static_assert(std::is_same<decltype(int_result(true)), int>::value, "Not the same type");
+///     }
+/// 
+
+#include <boost/hof/detail/callable_base.hpp>
+#include <boost/hof/is_invocable.hpp>
+#include <boost/hof/always.hpp>
+#include <boost/hof/reveal.hpp>
+
+namespace boost { namespace hof {
+
+template<class Result, class F>
+struct result_adaptor : detail::callable_base<F>
+{
+    BOOST_HOF_INHERIT_CONSTRUCTOR(result_adaptor, detail::callable_base<F>)
+
+    typedef Result result_type;
+
+    struct failure
+    : failure_for<detail::callable_base<F>>
+    {};
+
+    template<class... Ts>
+    constexpr const detail::callable_base<F>& base_function(Ts&&... xs) const
+    {
+        return boost::hof::always_ref(*this)(xs...);
+    }
+
+    template<class... Ts, class=typename std::enable_if<(boost::hof::is_invocable<F, Ts...>::value)>::type>
+    constexpr result_type operator()(Ts&&... xs) const
+    {
+        return this->base_function(xs...)(BOOST_HOF_FORWARD(Ts)(xs)...);
+    };
+};
+
+template<class F>
+struct result_adaptor<void, F> : detail::callable_base<F>
+{
+    BOOST_HOF_INHERIT_CONSTRUCTOR(result_adaptor, detail::callable_base<F>)
+
+    typedef void result_type;
+
+    template<class... Ts>
+    constexpr const detail::callable_base<F>& base_function(Ts&&... xs) const
+    {
+        return boost::hof::always_ref(*this)(xs...);
+    }
+
+    template<class... Ts, class=typename std::enable_if<(boost::hof::is_invocable<F, Ts...>::value)>::type>
+    constexpr typename detail::holder<Ts...>::type operator()(Ts&&... xs) const
+    {
+        return (typename detail::holder<Ts...>::type)this->base_function(xs...)(BOOST_HOF_FORWARD(Ts)(xs)...);
+    };
+};
+
+#if BOOST_HOF_HAS_VARIABLE_TEMPLATES
+namespace result_detail {
+template<class Result>
+struct result_f
+{
+    template<class F>
+    constexpr result_adaptor<Result, F> operator()(F f) const
+    {
+        return result_adaptor<Result, F>(boost::hof::move(f));
+    }
+};
+
+}
+
+template<class Result>
+static constexpr auto result = result_detail::result_f<Result>{};
+#else
+template<class Result, class F>
+constexpr result_adaptor<Result, F> result(F f)
+{
+    return result_adaptor<Result, F>(boost::hof::move(f));
+}
+#endif
+
+}} // namespace boost::hof
+
+#endif