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+/*=============================================================================
+ Copyright (c) 2015 Paul Fultz II
+ combine.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_COMBINE_H
+#define BOOST_HOF_GUARD_COMBINE_H
+
+/// combine
+/// =======
+///
+/// Description
+/// -----------
+///
+/// The `combine` function adaptor combines several functions together with
+/// their arguments. It essentially zips each function with an argument before
+/// calling the main function.
+///
+/// Synopsis
+/// --------
+///
+/// template<class F, class... Gs>
+/// constexpr combine_adaptor<F, Gs...> combine(F f, Gs... gs);
+///
+/// Semantics
+/// ---------
+///
+/// assert(combine(f, gs...)(xs...) == f(gs(xs)...));
+///
+/// Requirements
+/// ------------
+///
+/// F and Gs must be:
+///
+/// * [ConstInvocable](ConstInvocable)
+/// * MoveConstructible
+///
+/// Example
+/// -------
+///
+/// #include <boost/hof.hpp>
+/// #include <cassert>
+/// #include <tuple>
+/// #include <utility>
+///
+/// int main() {
+/// auto f = boost::hof::combine(
+/// boost::hof::construct<std::tuple>(),
+/// boost::hof::capture(1)(boost::hof::construct<std::pair>()),
+/// boost::hof::capture(2)(boost::hof::construct<std::pair>()));
+/// assert(f(3, 7) == std::make_tuple(std::make_pair(1, 3), std::make_pair(2, 7)));
+/// }
+///
+
+#include <boost/hof/pack.hpp>
+#include <boost/hof/always.hpp>
+#include <boost/hof/detail/callable_base.hpp>
+#include <boost/hof/detail/make.hpp>
+
+namespace boost { namespace hof { namespace detail {
+
+template<class S, class F, class... Gs>
+struct combine_adaptor_base;
+
+template<std::size_t... Ns, class F, class... Gs>
+struct combine_adaptor_base<seq<Ns...>, F, Gs...>
+: F, pack_base<seq<Ns...>, Gs...>
+{
+ typedef pack_base<seq<Ns...>, Gs...> base_type;
+
+ BOOST_HOF_INHERIT_DEFAULT(combine_adaptor_base, base_type, F)
+
+ template<class X, class... Xs,
+ BOOST_HOF_ENABLE_IF_CONSTRUCTIBLE(F, X),
+ BOOST_HOF_ENABLE_IF_CONSTRUCTIBLE(base_type, Xs...)>
+ constexpr combine_adaptor_base(X&& x, Xs&&... xs)
+ : F(BOOST_HOF_FORWARD(X)(x)), base_type(BOOST_HOF_FORWARD(Xs)(xs)...)
+ {}
+
+ template<class... Ts>
+ constexpr const F& base_function(Ts&&... xs) const
+ {
+ return boost::hof::always_ref(*this)(xs...);
+ }
+
+ BOOST_HOF_RETURNS_CLASS(combine_adaptor_base);
+
+// Result needs to be calculated in a separate class to avoid confusing the
+// compiler on MSVC
+#if BOOST_HOF_NO_EXPRESSION_SFINAE || BOOST_HOF_HAS_MANUAL_DEDUCTION
+ template<class... Ts>
+ struct combine_result
+ : result_of<const F&, result_of<const Gs&, id_<Ts>>...>
+ {};
+#endif
+
+ template<class... Ts>
+#if BOOST_HOF_NO_EXPRESSION_SFINAE || BOOST_HOF_HAS_MANUAL_DEDUCTION
+ constexpr typename combine_result<Ts...>::type
+#else
+ constexpr auto
+#endif
+ operator()(Ts&&... xs) const BOOST_HOF_SFINAE_MANUAL_RETURNS
+ (
+ (BOOST_HOF_MANGLE_CAST(const F&)(BOOST_HOF_CONST_THIS->base_function(xs...)))
+ (boost::hof::alias_value<pack_tag<seq<Ns>, Gs...>, Gs>(*BOOST_HOF_CONST_THIS, xs)(BOOST_HOF_FORWARD(Ts)(xs))...)
+ );
+};
+
+}
+
+template<class F, class... Gs>
+struct combine_adaptor
+: detail::combine_adaptor_base<typename detail::gens<sizeof...(Gs)>::type, detail::callable_base<F>, detail::callable_base<Gs>...>
+{
+ typedef detail::combine_adaptor_base<typename detail::gens<sizeof...(Gs)>::type, detail::callable_base<F>, detail::callable_base<Gs>...> base_type;
+ BOOST_HOF_INHERIT_CONSTRUCTOR(combine_adaptor, base_type)
+};
+
+BOOST_HOF_DECLARE_STATIC_VAR(combine, detail::make<combine_adaptor>);
+
+}} // namespace boost::hof
+
+#endif