/*=============================================================================
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Copyright (c) 2014 Paul Fultz II
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proj.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_ON_H
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#define BOOST_HOF_GUARD_FUNCTION_ON_H
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/// proj
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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 `proj` function adaptor applies a projection onto the parameters of
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/// another function. This is useful, for example, to define a function for
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/// sorting such that the ordering is based off of the value of one of its
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/// member fields.
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///
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/// Also, if just a projection is given, then the projection will be called
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/// for each of its arguments.
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///
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/// Note: All projections are always evaluated in order from left-to-right.
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///
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/// Synopsis
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/// --------
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///
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/// template<class Projection, class F>
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/// constexpr proj_adaptor<Projection, F> proj(Projection p, F f);
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///
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/// template<class Projection>
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/// constexpr proj_adaptor<Projection> proj(Projection p);
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///
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/// Semantics
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/// ---------
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///
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/// assert(proj(p, f)(xs...) == f(p(xs)...));
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/// assert(proj(p)(xs...) == p(xs)...);
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///
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/// Requirements
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/// ------------
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///
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/// Projection must be:
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///
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/// * [UnaryInvocable](UnaryInvocable)
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/// * MoveConstructible
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///
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/// F must be:
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///
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/// * [ConstInvocable](ConstInvocable)
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/// * MoveConstructible
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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 foo
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/// {
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/// foo(int x_) : x(x_)
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/// {}
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/// int x;
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/// };
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///
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/// int main() {
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/// assert(boost::hof::proj(&foo::x, _ + _)(foo(1), foo(2)) == 3);
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/// }
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///
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/// References
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/// ----------
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///
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/// * [Projections](Projections)
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/// * [Variadic print](<Variadic print>)
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///
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#include <utility>
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#include <boost/hof/always.hpp>
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#include <boost/hof/detail/callable_base.hpp>
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#include <boost/hof/detail/result_of.hpp>
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#include <boost/hof/detail/move.hpp>
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#include <boost/hof/detail/make.hpp>
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#include <boost/hof/detail/static_const_var.hpp>
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#include <boost/hof/detail/compressed_pair.hpp>
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#include <boost/hof/detail/result_type.hpp>
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#include <boost/hof/apply_eval.hpp>
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namespace boost { namespace hof {
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namespace detail {
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template<class T, class Projection>
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struct project_eval
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{
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T&& x;
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const Projection& p;
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template<class X, class P>
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constexpr project_eval(X&& xp, const P& pp) : x(BOOST_HOF_FORWARD(X)(xp)), p(pp)
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{}
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constexpr auto operator()() const BOOST_HOF_RETURNS
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(p(BOOST_HOF_FORWARD(T)(x)));
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};
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template<class T, class Projection>
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constexpr project_eval<T, Projection> make_project_eval(T&& x, const Projection& p)
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{
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return project_eval<T, Projection>(BOOST_HOF_FORWARD(T)(x), p);
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}
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template<class T, class Projection>
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struct project_void_eval
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{
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T&& x;
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const Projection& p;
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template<class X, class P>
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constexpr project_void_eval(X&& xp, const P& pp) : x(BOOST_HOF_FORWARD(X)(xp)), p(pp)
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{}
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struct void_ {};
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constexpr void_ operator()() const
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{
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return p(BOOST_HOF_FORWARD(T)(x)), void_();
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}
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};
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template<class T, class Projection>
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constexpr project_void_eval<T, Projection> make_project_void_eval(T&& x, const Projection& p)
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{
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return project_void_eval<T, Projection>(BOOST_HOF_FORWARD(T)(x), p);
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}
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template<class Projection, class F, class... Ts,
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class R=decltype(
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std::declval<const F&>()(std::declval<const Projection&>()(std::declval<Ts>())...)
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)>
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constexpr R by_eval(const Projection& p, const F& f, Ts&&... xs)
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{
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return boost::hof::apply_eval(f, make_project_eval(BOOST_HOF_FORWARD(Ts)(xs), p)...);
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}
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#if BOOST_HOF_NO_ORDERED_BRACE_INIT
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#define BOOST_HOF_BY_VOID_RETURN BOOST_HOF_ALWAYS_VOID_RETURN
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#else
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#if BOOST_HOF_NO_CONSTEXPR_VOID
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#define BOOST_HOF_BY_VOID_RETURN boost::hof::detail::swallow
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#else
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#define BOOST_HOF_BY_VOID_RETURN void
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#endif
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#endif
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template<class Projection, class... Ts>
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constexpr BOOST_HOF_ALWAYS_VOID_RETURN by_void_eval(const Projection& p, Ts&&... xs)
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{
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return boost::hof::apply_eval(boost::hof::always(), boost::hof::detail::make_project_void_eval(BOOST_HOF_FORWARD(Ts)(xs), p)...);
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}
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struct swallow
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{
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template<class... Ts>
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constexpr swallow(Ts&&...)
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{}
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};
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}
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template<class Projection, class F=void>
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struct proj_adaptor;
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template<class Projection, class F>
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struct proj_adaptor : detail::compressed_pair<detail::callable_base<Projection>, detail::callable_base<F>>, detail::function_result_type<F>
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{
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typedef proj_adaptor fit_rewritable_tag;
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typedef detail::compressed_pair<detail::callable_base<Projection>, detail::callable_base<F>> base;
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template<class... Ts>
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constexpr const detail::callable_base<F>& base_function(Ts&&... xs) const
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{
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return this->second(xs...);;
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}
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template<class... Ts>
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constexpr const detail::callable_base<Projection>& base_projection(Ts&&... xs) const
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{
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return this->first(xs...);
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}
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struct by_failure
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{
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template<class Failure>
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struct apply
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{
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template<class... Ts>
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struct of
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: Failure::template of<decltype(std::declval<detail::callable_base<Projection>>()(std::declval<Ts>()))...>
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{};
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};
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};
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struct failure
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: failure_map<by_failure, detail::callable_base<F>>
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{};
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BOOST_HOF_INHERIT_CONSTRUCTOR(proj_adaptor, base)
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BOOST_HOF_RETURNS_CLASS(proj_adaptor);
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template<class... Ts>
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constexpr BOOST_HOF_SFINAE_RESULT(const detail::callable_base<F>&, result_of<const detail::callable_base<Projection>&, id_<Ts>>...)
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operator()(Ts&&... xs) const BOOST_HOF_SFINAE_RETURNS
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(
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boost::hof::detail::by_eval(
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BOOST_HOF_MANGLE_CAST(const detail::callable_base<Projection>&)(BOOST_HOF_CONST_THIS->base_projection(xs...)),
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BOOST_HOF_MANGLE_CAST(const detail::callable_base<F>&)(BOOST_HOF_CONST_THIS->base_function(xs...)),
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BOOST_HOF_FORWARD(Ts)(xs)...
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)
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);
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};
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template<class Projection>
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struct proj_adaptor<Projection, void> : detail::callable_base<Projection>
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{
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typedef proj_adaptor fit_rewritable1_tag;
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template<class... Ts>
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constexpr const detail::callable_base<Projection>& base_projection(Ts&&... xs) const
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{
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return boost::hof::always_ref(*this)(xs...);
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}
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BOOST_HOF_INHERIT_DEFAULT(proj_adaptor, detail::callable_base<Projection>)
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template<class P, BOOST_HOF_ENABLE_IF_CONVERTIBLE(P, detail::callable_base<Projection>)>
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constexpr proj_adaptor(P&& p)
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: detail::callable_base<Projection>(BOOST_HOF_FORWARD(P)(p))
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{}
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BOOST_HOF_RETURNS_CLASS(proj_adaptor);
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template<class... Ts, class=detail::holder<decltype(std::declval<Projection>()(std::declval<Ts>()))...>>
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constexpr BOOST_HOF_BY_VOID_RETURN operator()(Ts&&... xs) const
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{
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#if BOOST_HOF_NO_ORDERED_BRACE_INIT
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return boost::hof::detail::by_void_eval(this->base_projection(xs...), BOOST_HOF_FORWARD(Ts)(xs)...);
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#else
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#if BOOST_HOF_NO_CONSTEXPR_VOID
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return
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#endif
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boost::hof::detail::swallow{
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(this->base_projection(xs...)(BOOST_HOF_FORWARD(Ts)(xs)), 0)...
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};
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#endif
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}
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};
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BOOST_HOF_DECLARE_STATIC_VAR(proj, detail::make<proj_adaptor>);
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}} // namespace boost::hof
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#endif
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