unpack.hpp
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/*=============================================================================
Copyright (c) 2015 Paul Fultz II
unpack.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_UNPACK_H
#define BOOST_HOF_GUARD_UNPACK_H
/// unpack
/// ======
///
/// Description
/// -----------
///
/// The `unpack` function adaptor takes a sequence and uses the elements of
/// the sequence for the arguments to the function. Multiple sequences can be
/// passed to the function. All elements from each sequence will be passed
/// into the function.
///
///
/// Synopsis
/// --------
///
/// template<class F>
/// unpack_adaptor<F> unpack(F f);
///
/// Requirements
/// ------------
///
/// F must be:
///
/// * [ConstInvocable](ConstInvocable)
/// * MoveConstructible
///
/// 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 = unpack(sum())(std::make_tuple(3,2));
/// assert(r == 5);
/// }
///
/// References
/// ----------
///
/// * [std::apply](http://en.cppreference.com/w/cpp/utility/apply) - C++17 function to unpack a tuple
/// * [`unpack_sequence`](unpack_sequence)
///
#include <boost/hof/unpack_sequence.hpp>
#include <boost/hof/is_unpackable.hpp>
#include <boost/hof/detail/seq.hpp>
#include <boost/hof/capture.hpp>
#include <boost/hof/always.hpp>
#include <boost/hof/reveal.hpp>
#include <boost/hof/detail/and.hpp>
#include <boost/hof/detail/delegate.hpp>
#include <boost/hof/detail/holder.hpp>
#include <boost/hof/detail/move.hpp>
#include <boost/hof/detail/make.hpp>
#include <boost/hof/detail/static_const_var.hpp>
namespace boost { namespace hof {
namespace detail {
template<class F, class Sequence>
constexpr auto unpack_simple(F&& f, Sequence&& s) BOOST_HOF_RETURNS
(
detail::unpack_impl(BOOST_HOF_FORWARD(F)(f), BOOST_HOF_FORWARD(Sequence)(s))
)
template<class F, class... Sequences>
constexpr auto unpack_join(F&& f, Sequences&&... s) BOOST_HOF_RETURNS
(
boost::hof::pack_join(unpack_simple(boost::hof::pack_forward, BOOST_HOF_FORWARD(Sequences)(s))...)(BOOST_HOF_FORWARD(F)(f))
);
}
template<class F>
struct unpack_adaptor : detail::callable_base<F>
{
typedef unpack_adaptor fit_rewritable1_tag;
BOOST_HOF_INHERIT_CONSTRUCTOR(unpack_adaptor, detail::callable_base<F>);
template<class... Ts>
constexpr const detail::callable_base<F>& base_function(Ts&&... xs) const noexcept
{
return boost::hof::always_ref(*this)(xs...);
}
struct unpack_failure
{
template<class Failure>
struct apply
{
struct deducer
{
template<class... Ts>
typename Failure::template of<Ts...> operator()(Ts&&...) const;
};
template<class T, class=typename std::enable_if<(
is_unpackable<T>::value
)>::type>
static auto deduce(T&& x)
BOOST_HOF_RETURNS
(
boost::hof::detail::unpack_simple(deducer(), BOOST_HOF_FORWARD(T)(x))
);
template<class T, class... Ts, class=typename std::enable_if<(
is_unpackable<T>::value && BOOST_HOF_AND_UNPACK(is_unpackable<Ts>::value)
)>::type>
static auto deduce(T&& x, Ts&&... xs) BOOST_HOF_RETURNS
(
boost::hof::detail::unpack_join(deducer(), BOOST_HOF_FORWARD(T)(x), BOOST_HOF_FORWARD(Ts)(xs)...)
);
#ifdef _MSC_VER
template<class... Ts>
struct nop_failure;
template<class... Ts, class=typename std::enable_if<(
!BOOST_HOF_AND_UNPACK(is_unpackable<Ts>::value)
)>::type>
static as_failure<nop_failure> deduce(Ts&&... xs);
#endif
template<class... Ts>
struct of
#if (defined(__GNUC__) && !defined (__clang__) && __GNUC__ == 4 && __GNUC_MINOR__ < 7) || defined (_MSC_VER)
: std::enable_if<true, decltype(apply::deduce(std::declval<Ts>()...))>::type
#else
: decltype(apply::deduce(std::declval<Ts>()...))
#endif
{};
};
};
struct failure
: failure_map<unpack_failure, detail::callable_base<F>>
{};
BOOST_HOF_RETURNS_CLASS(unpack_adaptor);
template<class T, class=typename std::enable_if<(
is_unpackable<T>::value
)>::type>
constexpr auto operator()(T&& x) const
BOOST_HOF_RETURNS
(
boost::hof::detail::unpack_simple(BOOST_HOF_MANGLE_CAST(const detail::callable_base<F>&)(BOOST_HOF_CONST_THIS->base_function(x)), BOOST_HOF_FORWARD(T)(x))
);
template<class T, class... Ts, class=typename std::enable_if<(
is_unpackable<T>::value && BOOST_HOF_AND_UNPACK(is_unpackable<Ts>::value)
)>::type>
constexpr auto operator()(T&& x, Ts&&... xs) const BOOST_HOF_RETURNS
(
boost::hof::detail::unpack_join(BOOST_HOF_MANGLE_CAST(const detail::callable_base<F>&)(BOOST_HOF_CONST_THIS->base_function(x)), BOOST_HOF_FORWARD(T)(x), BOOST_HOF_FORWARD(Ts)(xs)...)
);
};
BOOST_HOF_DECLARE_STATIC_VAR(unpack, detail::make<unpack_adaptor>);
}} // namespace boost::hof
#endif