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