63e88f80
 Hu Chunming
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/*!
@file
Defines `boost::hana::extend`.
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_EXTEND_HPP
#define BOOST_HANA_EXTEND_HPP
#include <boost/hana/fwd/extend.hpp>
#include <boost/hana/concept/comonad.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/duplicate.hpp>
#include <boost/hana/transform.hpp>
namespace boost { namespace hana {
//! @cond
template <typename W_, typename F>
constexpr decltype(auto) extend_t::operator()(W_&& w, F&& f) const {
using W = typename hana::tag_of<W_>::type;
using Extend = BOOST_HANA_DISPATCH_IF(extend_impl<W>,
hana::Comonad<W>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Comonad<W>::value,
"hana::extend(w, f) requires 'w' to be a Comonad");
#endif
return Extend::apply(static_cast<W_&&>(w), static_cast<F&&>(f));
}
//! @endcond
template <typename W, bool condition>
struct extend_impl<W, when<condition>> : default_ {
template <typename X, typename F>
static constexpr decltype(auto) apply(X&& x, F&& f) {
return hana::transform(hana::duplicate(static_cast<X&&>(x)),
static_cast<F&&>(f));
}
};
}} // end namespace boost::hana
#endif // !BOOST_HANA_EXTEND_HPP
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