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/*!
@file
Defines `boost::hana::tap`.
@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_TAP_HPP
#define BOOST_HANA_TAP_HPP
#include <boost/hana/fwd/tap.hpp>
#include <boost/hana/concept/monad.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/functional/partial.hpp>
#include <boost/hana/lift.hpp>
BOOST_HANA_NAMESPACE_BEGIN
template <typename M>
struct tap_t {
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Monad<M>::value,
"hana::tap<M> requires 'M' to be a Monad");
#endif
template <typename F>
constexpr auto operator()(F&& f) const {
using Tap = BOOST_HANA_DISPATCH_IF(tap_impl<M>,
hana::Monad<M>::value
);
return Tap::apply(static_cast<F&&>(f));
}
};
namespace detail {
template <typename M>
struct tap_helper {
template <typename F, typename X>
constexpr auto operator()(F&& f, X&& x) const {
(void)static_cast<F&&>(f)(x);
return hana::lift<M>(static_cast<X&&>(x));
}
};
}
template <typename M, bool condition>
struct tap_impl<M, when<condition>> : default_ {
template <typename F>
static constexpr auto apply(F&& f)
{ return hana::partial(detail::tap_helper<M>{}, static_cast<F&&>(f)); }
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_TAP_HPP
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