57 lines
1.8 KiB
C++
57 lines
1.8 KiB
C++
/*!
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@file
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Forward declares `boost::hana::default_` and `boost::hana::is_default`.
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Copyright Louis Dionne 2013-2022
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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_FWD_CORE_DEFAULT_HPP
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#define BOOST_HANA_FWD_CORE_DEFAULT_HPP
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#include <boost/hana/config.hpp>
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namespace boost { namespace hana {
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//! @ingroup group-core
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//! Mark a tag-dispatched method implementation as a default implementation.
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//!
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//! When defining a new concept with tag-dispatched methods, it is
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//! sometimes possible to provide a default implementation for some
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//! method(s). Making `default_` a base class of such a default
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//! implementation makes it possible to detect whether the method
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//! was dispatched to the default implementation afterwards.
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//!
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//!
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//! Example
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//! -------
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//! @include example/core/default.cpp
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struct default_ { };
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//! @ingroup group-core
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//! Returns whether a tag-dispatched method implementation is a default
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//! implementation.
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//!
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//! Given a tag-dispatched method implementation `method_impl<T...>`,
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//! `is_default<method_impl<T...>>` returns whether `method_impl<T...>`
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//! is a default implementation. Note that if there is no default
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//! implementation for the method, then `is_default` should not be
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//! used unless a static assertion saying that "the method is not
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//! implemented" is acceptable.
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//!
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//!
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//! Example
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//! -------
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//! @include example/core/default.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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template <typename Method>
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struct is_default { see documentation };
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#else
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template <typename T, typename = void>
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struct is_default;
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#endif
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}} // end namespace boost::hana
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#endif // !BOOST_HANA_FWD_CORE_DEFAULT_HPP
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