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