Edit: /usr/include/boost/hof/arg.hpp (3148B)
/*=============================================================================
Copyright (c) 2014 Paul Fultz II
arg.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_ARGS_H
#define BOOST_HOF_GUARD_FUNCTION_ARGS_H
#include
#include
#include
#include
/// arg
/// ===
///
/// Description
/// -----------
///
/// The `arg` function returns a function object that returns the Nth argument
/// passed to it. It actually starts at 1, so it is not the zero-based index
/// of the argument.
///
/// Synopsis
/// --------
///
/// template
/// constexpr auto arg(IntegralConstant);
///
/// template
/// constexpr auto arg_c(Ts&&...);
///
///
/// Example
/// -------
///
/// #include
/// #include
/// using namespace boost::hof;
///
/// int main() {
/// assert(arg(std::integral_constant())(1,2,3,4,5) == 3);
/// }
///
namespace boost { namespace hof {
namespace detail {
template
struct perfect_ref
{
typedef T type;
typedef typename std::remove_reference::type value_type;
T&& value;
constexpr perfect_ref(value_type& x) noexcept
: value(BOOST_HOF_FORWARD(T)(x))
{}
};
template
struct ignore
{
template
constexpr ignore(T&&...) noexcept
{}
};
template
struct args_at
{
template
constexpr auto operator()(ignore..., T x, Ts...) const
BOOST_HOF_RETURNS(BOOST_HOF_FORWARD(typename T::type)(x.value));
};
template
constexpr args_at make_args_at(seq) noexcept
{
return {};
}
template
constexpr auto get_args(Ts&&... xs) BOOST_HOF_RETURNS
(
boost::hof::detail::make_args_at(typename gens::type())(nullptr, BOOST_HOF_RETURNS_CONSTRUCT(perfect_ref)(xs)...)
);
template
struct make_args_f
{
template::type>
constexpr auto operator()(Ts&&... xs) const BOOST_HOF_RETURNS
(
boost::hof::detail::get_args(BOOST_HOF_FORWARD(Ts)(xs)...)
);
};
struct arg_f
{
template
constexpr make_args_f operator()(IntegralConstant) const noexcept
{
return make_args_f();
}
};
}
#if BOOST_HOF_HAS_VARIABLE_TEMPLATES
template
BOOST_HOF_STATIC_CONSTEXPR detail::make_args_f arg_c = {};
#else
template
constexpr auto arg_c(Ts&&... xs) BOOST_HOF_RETURNS
(
boost::hof::detail::get_args(BOOST_HOF_FORWARD(Ts)(xs)...)
);
#endif
BOOST_HOF_DECLARE_STATIC_VAR(arg, detail::arg_f);
}} // namespace boost::hof
#endif