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+/*=============================================================================
+ Copyright (c) 2015 Paul Fultz II
+ unpack.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_UNPACK_H
+#define BOOST_HOF_GUARD_UNPACK_H
+
+/// unpack
+/// ======
+///
+/// Description
+/// -----------
+///
+/// The `unpack` function adaptor takes a sequence and uses the elements of
+/// the sequence for the arguments to the function. Multiple sequences can be
+/// passed to the function. All elements from each sequence will be passed
+/// into the function.
+///
+///
+/// Synopsis
+/// --------
+///
+/// template<class F>
+/// unpack_adaptor<F> unpack(F f);
+///
+/// Requirements
+/// ------------
+///
+/// F must be:
+///
+/// * [ConstInvocable](ConstInvocable)
+/// * MoveConstructible
+///
+/// Example
+/// -------
+///
+/// #include <boost/hof.hpp>
+/// #include <cassert>
+/// using namespace boost::hof;
+///
+/// struct sum
+/// {
+/// template<class T, class U>
+/// T operator()(T x, U y) const
+/// {
+/// return x+y;
+/// }
+/// };
+///
+/// int main() {
+/// int r = unpack(sum())(std::make_tuple(3,2));
+/// assert(r == 5);
+/// }
+///
+/// References
+/// ----------
+///
+/// * [std::apply](http://en.cppreference.com/w/cpp/utility/apply) - C++17 function to unpack a tuple
+/// * [`unpack_sequence`](unpack_sequence)
+///
+
+#include <boost/hof/unpack_sequence.hpp>
+#include <boost/hof/is_unpackable.hpp>
+#include <boost/hof/detail/seq.hpp>
+#include <boost/hof/capture.hpp>
+#include <boost/hof/always.hpp>
+#include <boost/hof/reveal.hpp>
+#include <boost/hof/detail/and.hpp>
+#include <boost/hof/detail/delegate.hpp>
+#include <boost/hof/detail/holder.hpp>
+#include <boost/hof/detail/move.hpp>
+#include <boost/hof/detail/make.hpp>
+#include <boost/hof/detail/static_const_var.hpp>
+
+namespace boost { namespace hof {
+
+namespace detail {
+
+template<class F, class Sequence>
+constexpr auto unpack_simple(F&& f, Sequence&& s) BOOST_HOF_RETURNS
+(
+ detail::unpack_impl(BOOST_HOF_FORWARD(F)(f), BOOST_HOF_FORWARD(Sequence)(s))
+)
+
+template<class F, class... Sequences>
+constexpr auto unpack_join(F&& f, Sequences&&... s) BOOST_HOF_RETURNS
+(
+ boost::hof::pack_join(unpack_simple(boost::hof::pack_forward, BOOST_HOF_FORWARD(Sequences)(s))...)(BOOST_HOF_FORWARD(F)(f))
+);
+
+}
+
+template<class F>
+struct unpack_adaptor : detail::callable_base<F>
+{
+ typedef unpack_adaptor fit_rewritable1_tag;
+ BOOST_HOF_INHERIT_CONSTRUCTOR(unpack_adaptor, detail::callable_base<F>);
+
+ template<class... Ts>
+ constexpr const detail::callable_base<F>& base_function(Ts&&... xs) const noexcept
+ {
+ return boost::hof::always_ref(*this)(xs...);
+ }
+
+ struct unpack_failure
+ {
+ template<class Failure>
+ struct apply
+ {
+ struct deducer
+ {
+ template<class... Ts>
+ typename Failure::template of<Ts...> operator()(Ts&&...) const;
+ };
+
+ template<class T, class=typename std::enable_if<(
+ is_unpackable<T>::value
+ )>::type>
+ static auto deduce(T&& x)
+ BOOST_HOF_RETURNS
+ (
+ boost::hof::detail::unpack_simple(deducer(), BOOST_HOF_FORWARD(T)(x))
+ );
+
+ template<class T, class... Ts, class=typename std::enable_if<(
+ is_unpackable<T>::value && BOOST_HOF_AND_UNPACK(is_unpackable<Ts>::value)
+ )>::type>
+ static auto deduce(T&& x, Ts&&... xs) BOOST_HOF_RETURNS
+ (
+ boost::hof::detail::unpack_join(deducer(), BOOST_HOF_FORWARD(T)(x), BOOST_HOF_FORWARD(Ts)(xs)...)
+ );
+#ifdef _MSC_VER
+ template<class... Ts>
+ struct nop_failure;
+ template<class... Ts, class=typename std::enable_if<(
+ !BOOST_HOF_AND_UNPACK(is_unpackable<Ts>::value)
+ )>::type>
+ static as_failure<nop_failure> deduce(Ts&&... xs);
+#endif
+ template<class... Ts>
+ struct of
+#if (defined(__GNUC__) && !defined (__clang__) && __GNUC__ == 4 && __GNUC_MINOR__ < 7) || defined (_MSC_VER)
+ : std::enable_if<true, decltype(apply::deduce(std::declval<Ts>()...))>::type
+#else
+ : decltype(apply::deduce(std::declval<Ts>()...))
+#endif
+ {};
+ };
+ };
+
+ struct failure
+ : failure_map<unpack_failure, detail::callable_base<F>>
+ {};
+
+ BOOST_HOF_RETURNS_CLASS(unpack_adaptor);
+ template<class T, class=typename std::enable_if<(
+ is_unpackable<T>::value
+ )>::type>
+ constexpr auto operator()(T&& x) const
+ BOOST_HOF_RETURNS
+ (
+ boost::hof::detail::unpack_simple(BOOST_HOF_MANGLE_CAST(const detail::callable_base<F>&)(BOOST_HOF_CONST_THIS->base_function(x)), BOOST_HOF_FORWARD(T)(x))
+ );
+
+ template<class T, class... Ts, class=typename std::enable_if<(
+ is_unpackable<T>::value && BOOST_HOF_AND_UNPACK(is_unpackable<Ts>::value)
+ )>::type>
+ constexpr auto operator()(T&& x, Ts&&... xs) const BOOST_HOF_RETURNS
+ (
+ boost::hof::detail::unpack_join(BOOST_HOF_MANGLE_CAST(const detail::callable_base<F>&)(BOOST_HOF_CONST_THIS->base_function(x)), BOOST_HOF_FORWARD(T)(x), BOOST_HOF_FORWARD(Ts)(xs)...)
+ );
+};
+
+BOOST_HOF_DECLARE_STATIC_VAR(unpack, detail::make<unpack_adaptor>);
+
+}} // namespace boost::hof
+
+#endif