58 lines
1.6 KiB
C++
58 lines
1.6 KiB
C++
/*!
|
|
@file
|
|
Defines `boost::hana::length`.
|
|
|
|
@copyright Louis Dionne 2013-2016
|
|
Distributed under the Boost Software License, Version 1.0.
|
|
(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
|
|
*/
|
|
|
|
#ifndef BOOST_HANA_LENGTH_HPP
|
|
#define BOOST_HANA_LENGTH_HPP
|
|
|
|
#include <boost/hana/fwd/length.hpp>
|
|
|
|
#include <boost/hana/concept/foldable.hpp>
|
|
#include <boost/hana/config.hpp>
|
|
#include <boost/hana/core/dispatch.hpp>
|
|
#include <boost/hana/integral_constant.hpp>
|
|
#include <boost/hana/unpack.hpp>
|
|
|
|
|
|
BOOST_HANA_NAMESPACE_BEGIN
|
|
//! @cond
|
|
template <typename Xs>
|
|
constexpr auto length_t::operator()(Xs const& xs) const {
|
|
using S = typename hana::tag_of<Xs>::type;
|
|
using Length = BOOST_HANA_DISPATCH_IF(length_impl<S>,
|
|
hana::Foldable<S>::value
|
|
);
|
|
|
|
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
|
|
static_assert(hana::Foldable<S>::value,
|
|
"hana::length(xs) requires 'xs' to be Foldable");
|
|
#endif
|
|
|
|
return Length::apply(xs);
|
|
}
|
|
//! @endcond
|
|
|
|
namespace detail {
|
|
struct argn {
|
|
template <typename ...Xs>
|
|
constexpr hana::size_t<sizeof...(Xs)> operator()(Xs const& ...) const
|
|
{ return {}; }
|
|
};
|
|
}
|
|
|
|
template <typename T, bool condition>
|
|
struct length_impl<T, when<condition>> : default_ {
|
|
template <typename Xs>
|
|
static constexpr auto apply(Xs const& xs) {
|
|
return hana::unpack(xs, detail::argn{});
|
|
}
|
|
};
|
|
BOOST_HANA_NAMESPACE_END
|
|
|
|
#endif // !BOOST_HANA_LENGTH_HPP
|