63e88f80
 Hu Chunming
提交三方库
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/*=============================================================================
Copyright (c) 2015 Paul Fultz II
combine.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_COMBINE_H
#define BOOST_HOF_GUARD_COMBINE_H
/// combine
/// =======
///
/// Description
/// -----------
///
/// The `combine` function adaptor combines several functions together with
/// their arguments. It essentially zips each function with an argument before
/// calling the main function.
///
/// Synopsis
/// --------
///
/// template<class F, class... Gs>
/// constexpr combine_adaptor<F, Gs...> combine(F f, Gs... gs);
///
/// Semantics
/// ---------
///
/// assert(combine(f, gs...)(xs...) == f(gs(xs)...));
///
/// Requirements
/// ------------
///
/// F and Gs must be:
///
/// * [ConstInvocable](ConstInvocable)
/// * MoveConstructible
///
/// Example
/// -------
///
/// #include <boost/hof.hpp>
/// #include <cassert>
/// #include <tuple>
/// #include <utility>
///
/// int main() {
/// auto f = boost::hof::combine(
/// boost::hof::construct<std::tuple>(),
/// boost::hof::capture(1)(boost::hof::construct<std::pair>()),
/// boost::hof::capture(2)(boost::hof::construct<std::pair>()));
/// assert(f(3, 7) == std::make_tuple(std::make_pair(1, 3), std::make_pair(2, 7)));
/// }
///
#include <boost/hof/pack.hpp>
#include <boost/hof/always.hpp>
#include <boost/hof/detail/callable_base.hpp>
#include <boost/hof/detail/make.hpp>
namespace boost { namespace hof { namespace detail {
template<class S, class F, class... Gs>
struct combine_adaptor_base;
template<std::size_t... Ns, class F, class... Gs>
struct combine_adaptor_base<seq<Ns...>, F, Gs...>
: F, pack_base<seq<Ns...>, Gs...>
{
typedef pack_base<seq<Ns...>, Gs...> base_type;
BOOST_HOF_INHERIT_DEFAULT(combine_adaptor_base, base_type, F)
template<class X, class... Xs,
BOOST_HOF_ENABLE_IF_CONSTRUCTIBLE(F, X),
BOOST_HOF_ENABLE_IF_CONSTRUCTIBLE(base_type, Xs...)>
constexpr combine_adaptor_base(X&& x, Xs&&... xs)
: F(BOOST_HOF_FORWARD(X)(x)), base_type(BOOST_HOF_FORWARD(Xs)(xs)...)
{}
template<class... Ts>
constexpr const F& base_function(Ts&&... xs) const
{
return boost::hof::always_ref(*this)(xs...);
}
BOOST_HOF_RETURNS_CLASS(combine_adaptor_base);
// Result needs to be calculated in a separate class to avoid confusing the
// compiler on MSVC
#if BOOST_HOF_NO_EXPRESSION_SFINAE || BOOST_HOF_HAS_MANUAL_DEDUCTION
template<class... Ts>
struct combine_result
: result_of<const F&, result_of<const Gs&, id_<Ts>>...>
{};
#endif
template<class... Ts>
#if BOOST_HOF_NO_EXPRESSION_SFINAE || BOOST_HOF_HAS_MANUAL_DEDUCTION
constexpr typename combine_result<Ts...>::type
#else
constexpr auto
#endif
operator()(Ts&&... xs) const BOOST_HOF_SFINAE_MANUAL_RETURNS
(
(BOOST_HOF_MANGLE_CAST(const F&)(BOOST_HOF_CONST_THIS->base_function(xs...)))
(boost::hof::alias_value<pack_tag<seq<Ns>, Gs...>, Gs>(*BOOST_HOF_CONST_THIS, xs)(BOOST_HOF_FORWARD(Ts)(xs))...)
);
};
}
template<class F, class... Gs>
struct combine_adaptor
: detail::combine_adaptor_base<typename detail::gens<sizeof...(Gs)>::type, detail::callable_base<F>, detail::callable_base<Gs>...>
{
typedef detail::combine_adaptor_base<typename detail::gens<sizeof...(Gs)>::type, detail::callable_base<F>, detail::callable_base<Gs>...> base_type;
BOOST_HOF_INHERIT_CONSTRUCTOR(combine_adaptor, base_type)
};
BOOST_HOF_DECLARE_STATIC_VAR(combine, detail::make<combine_adaptor>);
}} // namespace boost::hof
#endif
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