Imported Upstream version 1.67.0upstream/1.67.0

1 files changed, 166 insertions, 0 deletions

diff --git a/boost/hof/flow.hpp b/boost/hof/flow.hpp
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+/*=============================================================================
+    Copyright (c) 2015 Paul Fultz II
+    flow.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_FUNCTION_FLOW_H
+#define BOOST_HOF_GUARD_FUNCTION_FLOW_H
+
+/// flow
+/// ====
+/// 
+/// Description
+/// -----------
+/// 
+/// The `flow` function adaptor provides function composition. It is useful as
+/// an alternative to using the pipe operator `|` when chaining functions. It is
+/// similiar to [`compose`](compose.md) except the evaluation order is
+/// reversed. So, `flow(f, g)(0)` is equivalent to `g(f(0))`.
+/// 
+/// 
+/// Synopsis
+/// --------
+/// 
+///     template<class... Fs>
+///     constexpr flow_adaptor<Fs...> flow(Fs... fs);
+/// 
+/// Semantics
+/// ---------
+/// 
+///     assert(flow(f, g)(xs...) == g(f(xs...)));
+/// 
+/// Requirements
+/// ------------
+/// 
+/// Fs must be:
+/// 
+/// * [ConstInvocable](ConstInvocable)
+/// * MoveConstructible
+/// 
+/// Example
+/// -------
+/// 
+///     #include <boost/hof.hpp>
+///     #include <cassert>
+///     using namespace boost::hof;
+/// 
+///     struct increment
+///     {
+///         template<class T>
+///         T operator()(T x) const
+///         {
+///             return x + 1;
+///         }
+///     };
+/// 
+///     struct decrement
+///     {
+///         template<class T>
+///         T operator()(T x) const
+///         {
+///             return x - 1;
+///         }
+///     };
+/// 
+///     int main() {
+///         int r = flow(increment(), decrement(), increment())(3);
+///         assert(r == 4);
+///     }
+/// 
+/// References
+/// ----------
+/// 
+/// * [Function composition](https://en.wikipedia.org/wiki/Function_composition)
+/// 
+
+#include <boost/hof/detail/callable_base.hpp>
+#include <boost/hof/always.hpp>
+#include <boost/hof/detail/delegate.hpp>
+#include <boost/hof/detail/compressed_pair.hpp>
+#include <boost/hof/detail/join.hpp>
+#include <tuple>
+#include <boost/hof/detail/move.hpp>
+#include <boost/hof/detail/make.hpp>
+#include <boost/hof/detail/result_type.hpp>
+#include <boost/hof/detail/static_const_var.hpp>
+
+namespace boost { namespace hof { namespace detail {
+
+template<class F1, class F2>
+struct flow_kernel : detail::compressed_pair<detail::callable_base<F1>, detail::callable_base<F2>>, compose_function_result_type<F2, F1>
+{
+    typedef detail::compressed_pair<detail::callable_base<F1>, detail::callable_base<F2>> base_type;
+
+    BOOST_HOF_INHERIT_CONSTRUCTOR(flow_kernel, base_type)
+
+    BOOST_HOF_RETURNS_CLASS(flow_kernel);
+
+    template<class... Ts>
+    constexpr BOOST_HOF_SFINAE_RESULT(const detail::callable_base<F2>&, result_of<const detail::callable_base<F1>&, id_<Ts>...>) 
+    operator()(Ts&&... xs) const BOOST_HOF_SFINAE_RETURNS
+    (
+        BOOST_HOF_MANGLE_CAST(const detail::callable_base<F2>&)(BOOST_HOF_CONST_THIS->second(xs...))(
+            BOOST_HOF_MANGLE_CAST(const detail::callable_base<F1>&)(BOOST_HOF_CONST_THIS->first(xs...))(BOOST_HOF_FORWARD(Ts)(xs)...)
+        )
+    );
+};
+}
+
+template<class F, class... Fs>
+struct flow_adaptor : detail::flow_kernel<F, BOOST_HOF_JOIN(flow_adaptor, Fs...)>
+{
+    typedef flow_adaptor fit_rewritable_tag;
+    typedef BOOST_HOF_JOIN(flow_adaptor, Fs...) tail;
+    typedef detail::flow_kernel<F, tail> base_type;
+
+    BOOST_HOF_INHERIT_DEFAULT(flow_adaptor, base_type)
+
+    template<class X, class... Xs, 
+        BOOST_HOF_ENABLE_IF_CONSTRUCTIBLE(detail::callable_base<F>, X), 
+        BOOST_HOF_ENABLE_IF_CONSTRUCTIBLE(tail, Xs...)
+    >
+    constexpr flow_adaptor(X&& f1, Xs&& ... fs) 
+    BOOST_HOF_NOEXCEPT(BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(base_type, X&&, tail) && BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(tail, Xs&&...))
+    : base_type(BOOST_HOF_FORWARD(X)(f1), tail(BOOST_HOF_FORWARD(Xs)(fs)...))
+    {}
+
+    template<class X,
+        BOOST_HOF_ENABLE_IF_CONSTRUCTIBLE(detail::callable_base<F>, X)
+    >
+    constexpr flow_adaptor(X&& f1) 
+    BOOST_HOF_NOEXCEPT_CONSTRUCTIBLE(base_type, X&&)
+    : base_type(BOOST_HOF_FORWARD(X)(f1))
+    {}
+};
+
+template<class F>
+struct flow_adaptor<F> : detail::callable_base<F>
+{
+    typedef flow_adaptor fit_rewritable_tag;
+    BOOST_HOF_INHERIT_DEFAULT(flow_adaptor, detail::callable_base<F>)
+
+    template<class X, BOOST_HOF_ENABLE_IF_CONVERTIBLE(X, detail::callable_base<F>)>
+    constexpr flow_adaptor(X&& f1) 
+    BOOST_HOF_NOEXCEPT_CONSTRUCTIBLE(detail::callable_base<F>, X&&)
+    : detail::callable_base<F>(BOOST_HOF_FORWARD(X)(f1))
+    {}
+
+};
+
+template<class F1, class F2>
+struct flow_adaptor<F1, F2>
+: detail::flow_kernel<detail::callable_base<F1>, detail::callable_base<F2>>
+{
+    typedef flow_adaptor fit_rewritable_tag;
+    typedef detail::flow_kernel<detail::callable_base<F1>, detail::callable_base<F2>> base_type;
+
+    BOOST_HOF_INHERIT_CONSTRUCTOR(flow_adaptor, base_type)
+};
+
+BOOST_HOF_DECLARE_STATIC_VAR(flow, detail::make<flow_adaptor>);
+
+}} // namespace boost::hof
+
+#endif