60 lines
1.6 KiB
C++
60 lines
1.6 KiB
C++
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/*!
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@file
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Defines `boost::hana::tap`.
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@copyright Louis Dionne 2013-2016
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_TAP_HPP
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#define BOOST_HANA_TAP_HPP
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#include <boost/hana/fwd/tap.hpp>
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#include <boost/hana/concept/monad.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/dispatch.hpp>
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#include <boost/hana/functional/partial.hpp>
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#include <boost/hana/lift.hpp>
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BOOST_HANA_NAMESPACE_BEGIN
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template <typename M>
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struct tap_t {
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Monad<M>::value,
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"hana::tap<M> requires 'M' to be a Monad");
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#endif
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template <typename F>
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constexpr auto operator()(F&& f) const {
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using Tap = BOOST_HANA_DISPATCH_IF(tap_impl<M>,
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hana::Monad<M>::value
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);
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return Tap::apply(static_cast<F&&>(f));
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}
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};
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namespace detail {
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template <typename M>
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struct tap_helper {
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template <typename F, typename X>
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constexpr auto operator()(F&& f, X&& x) const {
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(void)static_cast<F&&>(f)(x);
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return hana::lift<M>(static_cast<X&&>(x));
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}
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};
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}
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template <typename M, bool condition>
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struct tap_impl<M, when<condition>> : default_ {
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template <typename F>
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static constexpr auto apply(F&& f)
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{ return hana::partial(detail::tap_helper<M>{}, static_cast<F&&>(f)); }
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_TAP_HPP
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