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 Hu Chunming
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/*!
@file
Forward declares `boost::hana::contains` and `boost::hana::in`.
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_FWD_CONTAINS_HPP
#define BOOST_HANA_FWD_CONTAINS_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/core/when.hpp>
#include <boost/hana/functional/flip.hpp>
#include <boost/hana/functional/infix.hpp>
namespace boost { namespace hana {
//! Returns whether the key occurs in the structure.
//! @ingroup group-Searchable
//!
//! Given a `Searchable` structure `xs` and a `key`, `contains` returns
//! whether any of the keys of the structure is equal to the given `key`.
//! If the structure is not finite, an equal key has to appear at a finite
//! position in the structure for this method to finish. For convenience,
//! `contains` can also be applied in infix notation.
//!
//!
//! @param xs
//! The structure to search.
//!
//! @param key
//! A key to be searched for in the structure. The key has to be
//! `Comparable` with the other keys of the structure.
//!
//!
//! Example
//! -------
//! @include example/contains.cpp
#ifdef BOOST_HANA_DOXYGEN_INVOKED
constexpr auto contains = [](auto&& xs, auto&& key) {
return tag-dispatched;
};
#else
template <typename S, typename = void>
struct contains_impl : contains_impl<S, when<true>> { };
struct contains_t {
template <typename Xs, typename Key>
constexpr auto operator()(Xs&& xs, Key&& key) const;
};
BOOST_HANA_INLINE_VARIABLE constexpr auto contains = hana::infix(contains_t{});
#endif
//! Return whether the key occurs in the structure.
//! @ingroup group-Searchable
//!
//! Specifically, this is equivalent to `contains`, except `in` takes its
//! arguments in reverse order. Like `contains`, `in` can also be applied
//! in infix notation for increased expressiveness. This function is not a
//! method that can be overriden; it is just a convenience function
//! provided with the concept.
//!
//!
//! Example
//! -------
//! @include example/in.cpp
BOOST_HANA_INLINE_VARIABLE constexpr auto in = hana::infix(hana::flip(hana::contains));
}} // end namespace boost::hana
#endif // !BOOST_HANA_FWD_CONTAINS_HPP
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