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+/*=============================================================================
+ Copyright (c) 2014 Paul Fultz II
+ pack.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_PACK_H
+#define BOOST_HOF_GUARD_FUNCTION_PACK_H
+
+/// pack
+/// ====
+///
+/// Description
+/// -----------
+///
+/// The `pack` function returns a higher order function object that takes a
+/// function that will be passed the initial elements. The function object is
+/// a sequence that can be unpacked with `unpack_adaptor` as well. Also,
+/// `pack_join` can be used to join multiple packs together.
+///
+/// Synopsis
+/// --------
+///
+/// // Decay everything before capturing
+/// template<class... Ts>
+/// constexpr auto pack(Ts&&... xs);
+///
+/// // Capture lvalues by reference and rvalue reference by reference
+/// template<class... Ts>
+/// constexpr auto pack_forward(Ts&&... xs);
+///
+/// // Capture lvalues by reference and rvalues by value.
+/// template<class... Ts>
+/// constexpr auto pack_basic(Ts&&... xs);
+///
+/// // Join multiple packs together
+/// template<class... Ts>
+/// constexpr auto pack_join(Ts&&... xs);
+///
+/// Semantics
+/// ---------
+///
+/// assert(pack(xs...)(f) == f(xs...));
+/// assert(unpack(f)(pack(xs...)) == f(xs...));
+///
+/// assert(pack_join(pack(xs...), pack(ys...)) == pack(xs..., ys...));
+///
+///
+/// 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 = pack(3, 2)(sum());
+/// assert(r == 5);
+/// }
+///
+/// See Also
+/// --------
+///
+/// * [unpack](unpack)
+///
+
+#include <boost/hof/detail/seq.hpp>
+#include <boost/hof/detail/delegate.hpp>
+#include <boost/hof/detail/remove_rvalue_reference.hpp>
+#include <boost/hof/detail/unwrap.hpp>
+#include <boost/hof/detail/static_const_var.hpp>
+#include <boost/hof/unpack_sequence.hpp>
+#include <boost/hof/returns.hpp>
+#include <boost/hof/alias.hpp>
+#include <boost/hof/decay.hpp>
+
+namespace boost { namespace hof { namespace detail {
+
+template<class...>
+struct pack_tag
+{};
+
+template<class T, class Tag>
+struct pack_holder
+: detail::alias_empty<T, Tag>
+{};
+
+template<class Seq, class... Ts>
+struct pack_base;
+
+template<class T>
+struct is_copyable
+: std::integral_constant<bool, (
+ BOOST_HOF_IS_CONSTRUCTIBLE(T, const T&)
+)>
+{};
+
+template<class T>
+struct is_copyable<T&>
+: std::true_type
+{};
+
+template<class T>
+struct is_copyable<T&&>
+: std::true_type
+{};
+
+template<class T, class Tag, class X, class... Ts, typename std::enable_if<
+ is_copyable<T>::value && !std::is_lvalue_reference<T>::value
+, int>::type = 0>
+constexpr T pack_get(X&& x, Ts&&... xs) noexcept(BOOST_HOF_IS_NOTHROW_COPY_CONSTRUCTIBLE(T))
+{
+ return static_cast<T>(boost::hof::alias_value<Tag, T>(BOOST_HOF_FORWARD(X)(x), xs...));
+}
+
+template<class T, class Tag, class X, class... Ts, typename std::enable_if<
+ std::is_lvalue_reference<T>::value
+, int>::type = 0>
+constexpr T pack_get(X&& x, Ts&&... xs) noexcept
+{
+ return boost::hof::alias_value<Tag, T>(x, xs...);
+}
+
+template<class T, class Tag, class X, class... Ts, typename std::enable_if<
+ !is_copyable<T>::value
+, int>::type = 0>
+constexpr auto pack_get(X&& x, Ts&&... xs) BOOST_HOF_RETURNS
+(
+ boost::hof::alias_value<Tag, T>(BOOST_HOF_FORWARD(X)(x), xs...)
+);
+
+#if (defined(__GNUC__) && !defined (__clang__) && __GNUC__ == 4 && __GNUC_MINOR__ < 7) || defined(_MSC_VER)
+template<class... Ts>
+struct pack_holder_base
+: Ts::type...
+{
+ template<class... Xs, class=typename std::enable_if<(sizeof...(Xs) == sizeof...(Ts))>::type>
+ constexpr pack_holder_base(Xs&&... xs)
+ BOOST_HOF_NOEXCEPT(BOOST_HOF_AND_UNPACK(BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(typename Ts::type, Xs&&)))
+ : Ts::type(BOOST_HOF_FORWARD(Xs)(xs))...
+ {}
+#ifndef _MSC_VER
+ // BOOST_HOF_INHERIT_DEFAULT(pack_holder_base, typename std::remove_cv<typename std::remove_reference<typename Ts::type>::type>::type...)
+ BOOST_HOF_INHERIT_DEFAULT(pack_holder_base, typename Ts::type...)
+#endif
+};
+
+template<class T>
+struct pack_holder_base<T>
+: T::type
+{
+ typedef typename T::type base;
+ BOOST_HOF_INHERIT_CONSTRUCTOR(pack_holder_base, base);
+};
+
+template<class... Ts>
+struct pack_holder_builder
+{
+ template<class T, std::size_t N>
+ struct apply
+ : pack_holder<T, pack_tag<seq<N>, Ts...>>
+ {};
+};
+
+template<std::size_t... Ns, class... Ts>
+struct pack_base<seq<Ns...>, Ts...>
+: pack_holder_base<typename pack_holder_builder<Ts...>::template apply<Ts, Ns>...>
+{
+ typedef pack_holder_base<typename pack_holder_builder<Ts...>::template apply<Ts, Ns>...> base;
+ template<class X1, class X2, class... Xs>
+ constexpr pack_base(X1&& x1, X2&& x2, Xs&&... xs)
+ BOOST_HOF_NOEXCEPT(BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(base, X1&&, X2&&, Xs&...))
+ : base(BOOST_HOF_FORWARD(X1)(x1), BOOST_HOF_FORWARD(X2)(x2), BOOST_HOF_FORWARD(Xs)(xs)...)
+ {}
+
+ template<class X1, typename std::enable_if<(BOOST_HOF_IS_CONSTRUCTIBLE(base, X1)), int>::type = 0>
+ constexpr pack_base(X1&& x1)
+ BOOST_HOF_NOEXCEPT(BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(base, X1&&))
+ : base(BOOST_HOF_FORWARD(X1)(x1))
+ {}
+
+ // BOOST_HOF_INHERIT_DEFAULT(pack_base, typename std::remove_cv<typename std::remove_reference<Ts>::type>::type...);
+ BOOST_HOF_INHERIT_DEFAULT(pack_base, Ts...);
+
+ BOOST_HOF_RETURNS_CLASS(pack_base);
+
+ template<class F>
+ constexpr auto operator()(F&& f) const BOOST_HOF_RETURNS
+ (
+ f(boost::hof::detail::pack_get<Ts, pack_tag<seq<Ns>, Ts...>>(*BOOST_HOF_CONST_THIS, f)...)
+ );
+
+ typedef std::integral_constant<std::size_t, sizeof...(Ts)> fit_function_param_limit;
+
+ template<class F>
+ struct apply
+ : F::template apply<Ts...>
+ {};
+};
+
+template<class T>
+struct pack_base<seq<0>, T>
+: pack_holder_base<pack_holder<T, pack_tag<seq<0>, T>>>
+{
+ typedef pack_holder_base<pack_holder<T, pack_tag<seq<0>, T>>> base;
+
+ template<class X1, typename std::enable_if<(BOOST_HOF_IS_CONSTRUCTIBLE(base, X1)), int>::type = 0>
+ constexpr pack_base(X1&& x1)
+ BOOST_HOF_NOEXCEPT(BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(base, X1&&))
+ : base(BOOST_HOF_FORWARD(X1)(x1))
+ {}
+
+ BOOST_HOF_INHERIT_DEFAULT(pack_base, T);
+
+ BOOST_HOF_RETURNS_CLASS(pack_base);
+
+ template<class F>
+ constexpr auto operator()(F&& f) const BOOST_HOF_RETURNS
+ (
+ f(boost::hof::detail::pack_get<T, pack_tag<seq<0>, T>>(*BOOST_HOF_CONST_THIS, f))
+ );
+
+ typedef std::integral_constant<std::size_t, 1> fit_function_param_limit;
+
+ template<class F>
+ struct apply
+ : F::template apply<T>
+ {};
+};
+
+#else
+
+template<std::size_t... Ns, class... Ts>
+struct pack_base<seq<Ns...>, Ts...>
+: pack_holder<Ts, pack_tag<seq<Ns>, Ts...>>::type...
+{
+ // BOOST_HOF_INHERIT_DEFAULT(pack_base, typename std::remove_cv<typename std::remove_reference<Ts>::type>::type...);
+ BOOST_HOF_INHERIT_DEFAULT(pack_base, Ts...);
+
+ template<class... Xs, BOOST_HOF_ENABLE_IF_CONVERTIBLE_UNPACK(Xs&&, typename pack_holder<Ts, pack_tag<seq<Ns>, Ts...>>::type)>
+ constexpr pack_base(Xs&&... xs)
+ BOOST_HOF_NOEXCEPT(BOOST_HOF_AND_UNPACK(BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(typename pack_holder<Ts, pack_tag<seq<Ns>, Ts...>>::type, Xs&&)))
+ : pack_holder<Ts, pack_tag<seq<Ns>, Ts...>>::type(BOOST_HOF_FORWARD(Xs)(xs))...
+ {}
+
+ // typedef pack_base<seq<Ns...>, Ts...> self_t;
+
+ BOOST_HOF_RETURNS_CLASS(pack_base);
+
+ template<class F>
+ constexpr auto operator()(F&& f) const BOOST_HOF_RETURNS
+ (
+ f(boost::hof::detail::pack_get<Ts, pack_tag<seq<Ns>, Ts...>>(*BOOST_HOF_CONST_THIS, f)...)
+ );
+
+ typedef std::integral_constant<std::size_t, sizeof...(Ts)> fit_function_param_limit;
+
+ template<class F>
+ struct apply
+ : F::template apply<Ts...>
+ {};
+};
+
+#endif
+
+template<>
+struct pack_base<seq<> >
+{
+ template<class F>
+ constexpr auto operator()(F&& f) const BOOST_HOF_RETURNS
+ (f());
+
+ typedef std::integral_constant<std::size_t, 0> fit_function_param_limit;
+
+ template<class F>
+ struct apply
+ : F::template apply<>
+ {};
+};
+
+#define BOOST_HOF_DETAIL_UNPACK_PACK_BASE(ref, move) \
+template<class F, std::size_t... Ns, class... Ts> \
+constexpr auto unpack_pack_base(F&& f, pack_base<seq<Ns...>, Ts...> ref x) \
+BOOST_HOF_RETURNS(f(boost::hof::alias_value<pack_tag<seq<Ns>, Ts...>, Ts>(move(x), f)...))
+BOOST_HOF_UNARY_PERFECT_FOREACH(BOOST_HOF_DETAIL_UNPACK_PACK_BASE)
+
+template<class P1, class P2>
+struct pack_join_base;
+
+// TODO: Extend to join more than two packs at a time
+template<std::size_t... Ns1, class... Ts1, std::size_t... Ns2, class... Ts2>
+struct pack_join_base<pack_base<seq<Ns1...>, Ts1...>, pack_base<seq<Ns2...>, Ts2...>>
+{
+ static constexpr long total_size = sizeof...(Ts1) + sizeof...(Ts2);
+ typedef pack_base<typename detail::gens<total_size>::type, Ts1..., Ts2...> result_type;
+
+ template<class P1, class P2>
+ static constexpr result_type call(P1&& p1, P2&& p2)
+ BOOST_HOF_RETURNS_DEDUCE_NOEXCEPT(
+ result_type(
+ boost::hof::detail::pack_get<Ts1, pack_tag<seq<Ns1>, Ts1...>>(BOOST_HOF_FORWARD(P1)(p1))...,
+ boost::hof::detail::pack_get<Ts2, pack_tag<seq<Ns2>, Ts2...>>(BOOST_HOF_FORWARD(P2)(p2))...)
+ )
+ {
+ return result_type(
+ boost::hof::detail::pack_get<Ts1, pack_tag<seq<Ns1>, Ts1...>>(BOOST_HOF_FORWARD(P1)(p1))...,
+ boost::hof::detail::pack_get<Ts2, pack_tag<seq<Ns2>, Ts2...>>(BOOST_HOF_FORWARD(P2)(p2))...);
+ }
+};
+
+template<class P1, class P2>
+struct pack_join_result
+: pack_join_base<
+ typename std::remove_cv<typename std::remove_reference<P1>::type>::type,
+ typename std::remove_cv<typename std::remove_reference<P2>::type>::type
+>
+{};
+
+
+struct pack_basic_f
+{
+ template<class... Ts>
+ constexpr auto operator()(Ts&&... xs) const BOOST_HOF_RETURNS
+ (
+ pack_base<typename gens<sizeof...(Ts)>::type, typename remove_rvalue_reference<Ts>::type...>(BOOST_HOF_FORWARD(Ts)(xs)...)
+ );
+};
+
+struct pack_forward_f
+{
+ template<class... Ts>
+ constexpr auto operator()(Ts&&... xs) const BOOST_HOF_RETURNS
+ (
+ pack_base<typename gens<sizeof...(Ts)>::type, Ts&&...>(BOOST_HOF_FORWARD(Ts)(xs)...)
+ );
+};
+
+struct pack_f
+{
+ template<class... Ts>
+ constexpr auto operator()(Ts&&... xs) const BOOST_HOF_RETURNS
+ (
+ pack_basic_f()(boost::hof::decay(BOOST_HOF_FORWARD(Ts)(xs))...)
+ );
+};
+
+template<class P1, class P2>
+constexpr typename pack_join_result<P1, P2>::result_type make_pack_join_dual(P1&& p1, P2&& p2)
+BOOST_HOF_RETURNS_DEDUCE_NOEXCEPT(pack_join_result<P1, P2>::call(BOOST_HOF_FORWARD(P1)(p1), BOOST_HOF_FORWARD(P2)(p2)))
+{
+ return pack_join_result<P1, P2>::call(BOOST_HOF_FORWARD(P1)(p1), BOOST_HOF_FORWARD(P2)(p2));
+}
+
+// Manually compute join return type to make older gcc happy
+template<class... Ts>
+struct join_type;
+
+template<class T>
+struct join_type<T>
+{
+ typedef T type;
+};
+
+template<class T, class... Ts>
+struct join_type<T, Ts...>
+{
+ typedef typename pack_join_result<T, typename join_type<Ts...>::type>::result_type type;
+};
+
+template<class P1>
+constexpr P1 make_pack_join(P1&& p1) BOOST_HOF_NOEXCEPT_CONSTRUCTIBLE(P1, P1&&)
+{
+ return BOOST_HOF_FORWARD(P1)(p1);
+}
+
+template<class P1, class... Ps>
+constexpr typename join_type<P1, Ps...>::type make_pack_join(P1&& p1, Ps&&... ps)
+BOOST_HOF_RETURNS_DEDUCE_NOEXCEPT(make_pack_join_dual(BOOST_HOF_FORWARD(P1)(p1), make_pack_join(BOOST_HOF_FORWARD(Ps)(ps)...)))
+{
+ return make_pack_join_dual(BOOST_HOF_FORWARD(P1)(p1), make_pack_join(BOOST_HOF_FORWARD(Ps)(ps)...));
+}
+
+struct pack_join_f
+{
+
+ template<class... Ps>
+ constexpr auto operator()(Ps&&... ps) const BOOST_HOF_RETURNS
+ (
+ make_pack_join(BOOST_HOF_FORWARD(Ps)(ps)...)
+ );
+};
+
+}
+
+BOOST_HOF_DECLARE_STATIC_VAR(pack_basic, detail::pack_basic_f);
+BOOST_HOF_DECLARE_STATIC_VAR(pack_forward, detail::pack_forward_f);
+BOOST_HOF_DECLARE_STATIC_VAR(pack, detail::pack_f);
+
+BOOST_HOF_DECLARE_STATIC_VAR(pack_join, detail::pack_join_f);
+
+template<class T, class... Ts>
+struct unpack_sequence<detail::pack_base<T, Ts...>>
+{
+ template<class F, class P>
+ constexpr static auto apply(F&& f, P&& p) BOOST_HOF_RETURNS
+ (
+ boost::hof::detail::unpack_pack_base(BOOST_HOF_FORWARD(F)(f), BOOST_HOF_FORWARD(P)(p))
+ );
+};
+
+}} // namespace boost::hof
+
+#endif
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