/*=============================================================================
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Copyright (c) 2014 Paul Fultz II
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pack.h
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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==============================================================================*/
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#ifndef BOOST_HOF_GUARD_FUNCTION_PACK_H
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#define BOOST_HOF_GUARD_FUNCTION_PACK_H
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/// pack
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/// ====
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///
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/// Description
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/// -----------
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///
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/// The `pack` function returns a higher order function object that takes a
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/// function that will be passed the initial elements. The function object is
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/// a sequence that can be unpacked with `unpack_adaptor` as well. Also,
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/// `pack_join` can be used to join multiple packs together.
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///
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/// Synopsis
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/// --------
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///
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/// // Decay everything before capturing
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/// template<class... Ts>
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/// constexpr auto pack(Ts&&... xs);
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///
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/// // Capture lvalues by reference and rvalue reference by reference
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/// template<class... Ts>
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/// constexpr auto pack_forward(Ts&&... xs);
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///
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/// // Capture lvalues by reference and rvalues by value.
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/// template<class... Ts>
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/// constexpr auto pack_basic(Ts&&... xs);
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///
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/// // Join multiple packs together
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/// template<class... Ts>
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/// constexpr auto pack_join(Ts&&... xs);
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///
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/// Semantics
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/// ---------
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///
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/// assert(pack(xs...)(f) == f(xs...));
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/// assert(unpack(f)(pack(xs...)) == f(xs...));
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///
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/// assert(pack_join(pack(xs...), pack(ys...)) == pack(xs..., ys...));
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///
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///
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/// Example
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/// -------
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///
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/// #include <boost/hof.hpp>
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/// #include <cassert>
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/// using namespace boost::hof;
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///
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/// struct sum
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/// {
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/// template<class T, class U>
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/// T operator()(T x, U y) const
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/// {
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/// return x+y;
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/// }
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/// };
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///
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/// int main() {
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/// int r = pack(3, 2)(sum());
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/// assert(r == 5);
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/// }
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///
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/// See Also
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/// --------
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///
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/// * [unpack](unpack)
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///
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#include <boost/hof/detail/seq.hpp>
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#include <boost/hof/detail/delegate.hpp>
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#include <boost/hof/detail/remove_rvalue_reference.hpp>
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#include <boost/hof/detail/unwrap.hpp>
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#include <boost/hof/detail/static_const_var.hpp>
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#include <boost/hof/unpack_sequence.hpp>
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#include <boost/hof/returns.hpp>
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#include <boost/hof/alias.hpp>
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#include <boost/hof/decay.hpp>
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namespace boost { namespace hof { namespace detail {
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template<class...>
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struct pack_tag
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{};
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template<class T, class Tag>
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struct pack_holder
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: detail::alias_empty<T, Tag>
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{};
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template<class Seq, class... Ts>
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struct pack_base;
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template<class T>
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struct is_copyable
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: std::integral_constant<bool, (
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BOOST_HOF_IS_CONSTRUCTIBLE(T, const T&)
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)>
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{};
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template<class T>
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struct is_copyable<T&>
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: std::true_type
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{};
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template<class T>
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struct is_copyable<T&&>
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: std::true_type
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{};
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template<class T, class Tag, class X, class... Ts, typename std::enable_if<
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is_copyable<T>::value && !std::is_lvalue_reference<T>::value
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, int>::type = 0>
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constexpr T pack_get(X&& x, Ts&&... xs) noexcept(BOOST_HOF_IS_NOTHROW_COPY_CONSTRUCTIBLE(T))
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{
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return static_cast<T>(boost::hof::alias_value<Tag, T>(BOOST_HOF_FORWARD(X)(x), xs...));
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}
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template<class T, class Tag, class X, class... Ts, typename std::enable_if<
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std::is_lvalue_reference<T>::value
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, int>::type = 0>
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constexpr T pack_get(X&& x, Ts&&... xs) noexcept
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{
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return boost::hof::alias_value<Tag, T>(x, xs...);
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}
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template<class T, class Tag, class X, class... Ts, typename std::enable_if<
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!is_copyable<T>::value
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, int>::type = 0>
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constexpr auto pack_get(X&& x, Ts&&... xs) BOOST_HOF_RETURNS
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(
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boost::hof::alias_value<Tag, T>(BOOST_HOF_FORWARD(X)(x), xs...)
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);
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#if (defined(__GNUC__) && !defined (__clang__) && __GNUC__ == 4 && __GNUC_MINOR__ < 7) || defined(_MSC_VER)
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template<class... Ts>
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struct pack_holder_base
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: Ts::type...
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{
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template<class... Xs, class=typename std::enable_if<(sizeof...(Xs) == sizeof...(Ts))>::type>
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constexpr pack_holder_base(Xs&&... xs)
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BOOST_HOF_NOEXCEPT(BOOST_HOF_AND_UNPACK(BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(typename Ts::type, Xs&&)))
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: Ts::type(BOOST_HOF_FORWARD(Xs)(xs))...
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{}
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#ifndef _MSC_VER
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// BOOST_HOF_INHERIT_DEFAULT(pack_holder_base, typename std::remove_cv<typename std::remove_reference<typename Ts::type>::type>::type...)
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BOOST_HOF_INHERIT_DEFAULT(pack_holder_base, typename Ts::type...)
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#endif
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};
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template<class T>
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struct pack_holder_base<T>
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: T::type
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{
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typedef typename T::type base;
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BOOST_HOF_INHERIT_CONSTRUCTOR(pack_holder_base, base);
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};
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template<class... Ts>
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struct pack_holder_builder
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{
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template<class T, std::size_t N>
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struct apply
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: pack_holder<T, pack_tag<seq<N>, Ts...>>
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{};
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};
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template<std::size_t... Ns, class... Ts>
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struct pack_base<seq<Ns...>, Ts...>
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: pack_holder_base<typename pack_holder_builder<Ts...>::template apply<Ts, Ns>...>
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{
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typedef pack_holder_base<typename pack_holder_builder<Ts...>::template apply<Ts, Ns>...> base;
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template<class X1, class X2, class... Xs>
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constexpr pack_base(X1&& x1, X2&& x2, Xs&&... xs)
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BOOST_HOF_NOEXCEPT(BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(base, X1&&, X2&&, Xs&...))
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: base(BOOST_HOF_FORWARD(X1)(x1), BOOST_HOF_FORWARD(X2)(x2), BOOST_HOF_FORWARD(Xs)(xs)...)
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{}
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template<class X1, typename std::enable_if<(BOOST_HOF_IS_CONSTRUCTIBLE(base, X1)), int>::type = 0>
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constexpr pack_base(X1&& x1)
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BOOST_HOF_NOEXCEPT(BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(base, X1&&))
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: base(BOOST_HOF_FORWARD(X1)(x1))
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{}
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// BOOST_HOF_INHERIT_DEFAULT(pack_base, typename std::remove_cv<typename std::remove_reference<Ts>::type>::type...);
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BOOST_HOF_INHERIT_DEFAULT(pack_base, Ts...);
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BOOST_HOF_RETURNS_CLASS(pack_base);
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template<class F>
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constexpr auto operator()(F&& f) const BOOST_HOF_RETURNS
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(
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f(boost::hof::detail::pack_get<Ts, pack_tag<seq<Ns>, Ts...>>(*BOOST_HOF_CONST_THIS, f)...)
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);
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typedef std::integral_constant<std::size_t, sizeof...(Ts)> fit_function_param_limit;
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template<class F>
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struct apply
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: F::template apply<Ts...>
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{};
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};
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template<class T>
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struct pack_base<seq<0>, T>
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: pack_holder_base<pack_holder<T, pack_tag<seq<0>, T>>>
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{
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typedef pack_holder_base<pack_holder<T, pack_tag<seq<0>, T>>> base;
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template<class X1, typename std::enable_if<(BOOST_HOF_IS_CONSTRUCTIBLE(base, X1)), int>::type = 0>
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constexpr pack_base(X1&& x1)
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BOOST_HOF_NOEXCEPT(BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(base, X1&&))
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: base(BOOST_HOF_FORWARD(X1)(x1))
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{}
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BOOST_HOF_INHERIT_DEFAULT(pack_base, T);
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BOOST_HOF_RETURNS_CLASS(pack_base);
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template<class F>
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constexpr auto operator()(F&& f) const BOOST_HOF_RETURNS
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(
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f(boost::hof::detail::pack_get<T, pack_tag<seq<0>, T>>(*BOOST_HOF_CONST_THIS, f))
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);
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typedef std::integral_constant<std::size_t, 1> fit_function_param_limit;
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template<class F>
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struct apply
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: F::template apply<T>
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{};
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};
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#else
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template<std::size_t... Ns, class... Ts>
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struct pack_base<seq<Ns...>, Ts...>
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: pack_holder<Ts, pack_tag<seq<Ns>, Ts...>>::type...
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{
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// BOOST_HOF_INHERIT_DEFAULT(pack_base, typename std::remove_cv<typename std::remove_reference<Ts>::type>::type...);
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BOOST_HOF_INHERIT_DEFAULT(pack_base, Ts...);
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template<class... Xs, BOOST_HOF_ENABLE_IF_CONVERTIBLE_UNPACK(Xs&&, typename pack_holder<Ts, pack_tag<seq<Ns>, Ts...>>::type)>
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constexpr pack_base(Xs&&... xs)
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BOOST_HOF_NOEXCEPT(BOOST_HOF_AND_UNPACK(BOOST_HOF_IS_NOTHROW_CONSTRUCTIBLE(typename pack_holder<Ts, pack_tag<seq<Ns>, Ts...>>::type, Xs&&)))
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: pack_holder<Ts, pack_tag<seq<Ns>, Ts...>>::type(BOOST_HOF_FORWARD(Xs)(xs))...
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{}
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// typedef pack_base<seq<Ns...>, Ts...> self_t;
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BOOST_HOF_RETURNS_CLASS(pack_base);
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template<class F>
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constexpr auto operator()(F&& f) const BOOST_HOF_RETURNS
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(
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f(boost::hof::detail::pack_get<Ts, pack_tag<seq<Ns>, Ts...>>(*BOOST_HOF_CONST_THIS, f)...)
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);
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typedef std::integral_constant<std::size_t, sizeof...(Ts)> fit_function_param_limit;
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template<class F>
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struct apply
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: F::template apply<Ts...>
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{};
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};
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#endif
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template<>
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struct pack_base<seq<> >
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{
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template<class F>
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constexpr auto operator()(F&& f) const BOOST_HOF_RETURNS
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(f());
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typedef std::integral_constant<std::size_t, 0> fit_function_param_limit;
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template<class F>
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struct apply
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: F::template apply<>
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{};
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};
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#define BOOST_HOF_DETAIL_UNPACK_PACK_BASE(ref, move) \
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template<class F, std::size_t... Ns, class... Ts> \
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constexpr auto unpack_pack_base(F&& f, pack_base<seq<Ns...>, Ts...> ref x) \
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BOOST_HOF_RETURNS(f(boost::hof::alias_value<pack_tag<seq<Ns>, Ts...>, Ts>(move(x), f)...))
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BOOST_HOF_UNARY_PERFECT_FOREACH(BOOST_HOF_DETAIL_UNPACK_PACK_BASE)
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template<class P1, class P2>
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struct pack_join_base;
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// TODO: Extend to join more than two packs at a time
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template<std::size_t... Ns1, class... Ts1, std::size_t... Ns2, class... Ts2>
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struct pack_join_base<pack_base<seq<Ns1...>, Ts1...>, pack_base<seq<Ns2...>, Ts2...>>
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{
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static constexpr long total_size = sizeof...(Ts1) + sizeof...(Ts2);
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typedef pack_base<typename detail::gens<total_size>::type, Ts1..., Ts2...> result_type;
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template<class P1, class P2>
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static constexpr result_type call(P1&& p1, P2&& p2)
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BOOST_HOF_RETURNS_DEDUCE_NOEXCEPT(
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result_type(
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boost::hof::detail::pack_get<Ts1, pack_tag<seq<Ns1>, Ts1...>>(BOOST_HOF_FORWARD(P1)(p1))...,
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boost::hof::detail::pack_get<Ts2, pack_tag<seq<Ns2>, Ts2...>>(BOOST_HOF_FORWARD(P2)(p2))...)
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)
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{
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return result_type(
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boost::hof::detail::pack_get<Ts1, pack_tag<seq<Ns1>, Ts1...>>(BOOST_HOF_FORWARD(P1)(p1))...,
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boost::hof::detail::pack_get<Ts2, pack_tag<seq<Ns2>, Ts2...>>(BOOST_HOF_FORWARD(P2)(p2))...);
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}
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};
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template<class P1, class P2>
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struct pack_join_result
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: pack_join_base<
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typename std::remove_cv<typename std::remove_reference<P1>::type>::type,
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typename std::remove_cv<typename std::remove_reference<P2>::type>::type
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>
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{};
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struct pack_basic_f
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{
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template<class... Ts>
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constexpr auto operator()(Ts&&... xs) const BOOST_HOF_RETURNS
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(
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pack_base<typename gens<sizeof...(Ts)>::type, typename remove_rvalue_reference<Ts>::type...>(BOOST_HOF_FORWARD(Ts)(xs)...)
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);
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};
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struct pack_forward_f
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{
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template<class... Ts>
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constexpr auto operator()(Ts&&... xs) const BOOST_HOF_RETURNS
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(
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pack_base<typename gens<sizeof...(Ts)>::type, Ts&&...>(BOOST_HOF_FORWARD(Ts)(xs)...)
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);
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};
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struct pack_f
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{
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template<class... Ts>
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constexpr auto operator()(Ts&&... xs) const BOOST_HOF_RETURNS
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(
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pack_basic_f()(boost::hof::decay(BOOST_HOF_FORWARD(Ts)(xs))...)
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);
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};
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template<class P1, class P2>
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constexpr typename pack_join_result<P1, P2>::result_type make_pack_join_dual(P1&& p1, P2&& p2)
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BOOST_HOF_RETURNS_DEDUCE_NOEXCEPT(pack_join_result<P1, P2>::call(BOOST_HOF_FORWARD(P1)(p1), BOOST_HOF_FORWARD(P2)(p2)))
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{
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return pack_join_result<P1, P2>::call(BOOST_HOF_FORWARD(P1)(p1), BOOST_HOF_FORWARD(P2)(p2));
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}
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// Manually compute join return type to make older gcc happy
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template<class... Ts>
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struct join_type;
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template<class T>
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struct join_type<T>
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{
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typedef T type;
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};
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template<class T, class... Ts>
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struct join_type<T, Ts...>
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{
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typedef typename pack_join_result<T, typename join_type<Ts...>::type>::result_type type;
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};
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template<class P1>
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constexpr P1 make_pack_join(P1&& p1) BOOST_HOF_NOEXCEPT_CONSTRUCTIBLE(P1, P1&&)
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{
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return BOOST_HOF_FORWARD(P1)(p1);
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}
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template<class P1, class... Ps>
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constexpr typename join_type<P1, Ps...>::type make_pack_join(P1&& p1, Ps&&... ps)
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BOOST_HOF_RETURNS_DEDUCE_NOEXCEPT(make_pack_join_dual(BOOST_HOF_FORWARD(P1)(p1), make_pack_join(BOOST_HOF_FORWARD(Ps)(ps)...)))
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{
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return make_pack_join_dual(BOOST_HOF_FORWARD(P1)(p1), make_pack_join(BOOST_HOF_FORWARD(Ps)(ps)...));
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}
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struct pack_join_f
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{
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template<class... Ps>
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constexpr auto operator()(Ps&&... ps) const BOOST_HOF_RETURNS
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(
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make_pack_join(BOOST_HOF_FORWARD(Ps)(ps)...)
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);
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};
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}
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BOOST_HOF_DECLARE_STATIC_VAR(pack_basic, detail::pack_basic_f);
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BOOST_HOF_DECLARE_STATIC_VAR(pack_forward, detail::pack_forward_f);
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BOOST_HOF_DECLARE_STATIC_VAR(pack, detail::pack_f);
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BOOST_HOF_DECLARE_STATIC_VAR(pack_join, detail::pack_join_f);
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template<class T, class... Ts>
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struct unpack_sequence<detail::pack_base<T, Ts...>>
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{
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template<class F, class P>
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constexpr static auto apply(F&& f, P&& p) BOOST_HOF_RETURNS
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(
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boost::hof::detail::unpack_pack_base(BOOST_HOF_FORWARD(F)(f), BOOST_HOF_FORWARD(P)(p))
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);
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};
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}} // namespace boost::hof
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#endif
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