598bfd3f
 Hu Chunming
提交_GLIBCXX_USE_CX...
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/*!
@file
Defines `boost::hana::duplicate`.
Copyright Louis Dionne 2013-2022
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_DUPLICATE_HPP
#define BOOST_HANA_DUPLICATE_HPP
#include <boost/hana/fwd/duplicate.hpp>
#include <boost/hana/concept/comonad.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/extend.hpp>
#include <boost/hana/functional/id.hpp>
namespace boost { namespace hana {
//! @cond
template <typename W_>
constexpr decltype(auto) duplicate_t::operator()(W_&& w) const {
using W = typename hana::tag_of<W_>::type;
using Duplicate = BOOST_HANA_DISPATCH_IF(duplicate_impl<W>,
hana::Comonad<W>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Comonad<W>::value,
"hana::duplicate(w) requires 'w' to be a Comonad");
#endif
return Duplicate::apply(static_cast<W_&&>(w));
}
//! @endcond
template <typename W, bool condition>
struct duplicate_impl<W, when<condition>> : default_ {
template <typename X>
static constexpr decltype(auto) apply(X&& x)
{ return hana::extend(static_cast<X&&>(x), hana::id); }
};
}} // end namespace boost::hana
#endif // !BOOST_HANA_DUPLICATE_HPP
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