hana/fwd/contains.hpp

0001 /*!
0002 @file
0003 Forward declares `boost::hana::contains` and `boost::hana::in`.
0004
0005 Copyright Louis Dionne 2013-2022
0006 Distributed under the Boost Software License, Version 1.0.
0007 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
0008  */
0009
0010 #ifndef BOOST_HANA_FWD_CONTAINS_HPP
0011 #define BOOST_HANA_FWD_CONTAINS_HPP
0012
0013 #include <boost/hana/config.hpp>
0014 #include <boost/hana/core/when.hpp>
0015 #include <boost/hana/functional/flip.hpp>
0016 #include <boost/hana/functional/infix.hpp>
0017
0018
0019 namespace boost { namespace hana {
0020     //! Returns whether the key occurs in the structure.
0021     //! @ingroup group-Searchable
0022     //!
0023     //! Given a `Searchable` structure `xs` and a `key`, `contains` returns
0024     //! whether any of the keys of the structure is equal to the given `key`.
0025     //! If the structure is not finite, an equal key has to appear at a finite
0026     //! position in the structure for this method to finish. For convenience,
0027     //! `contains` can also be applied in infix notation.
0028     //!
0029     //!
0030     //! @param xs
0031     //! The structure to search.
0032     //!
0033     //! @param key
0034     //! A key to be searched for in the structure. The key has to be
0035     //! `Comparable` with the other keys of the structure.
0036     //!
0037     //!
0038     //! Example
0039     //! -------
0040     //! @include example/contains.cpp
0041 #ifdef BOOST_HANA_DOXYGEN_INVOKED
0042     constexpr auto contains = [](auto&& xs, auto&& key) {
0043         return tag-dispatched;
0044     };
0045 #else
0046     template <typename S, typename = void>
0047     struct contains_impl : contains_impl<S, when<true>> { };
0048
0049     struct contains_t {
0050         template <typename Xs, typename Key>
0051         constexpr auto operator()(Xs&& xs, Key&& key) const;
0052     };
0053
0054     BOOST_HANA_INLINE_VARIABLE constexpr auto contains = hana::infix(contains_t{});
0055 #endif
0056
0057     //! Return whether the key occurs in the structure.
0058     //! @ingroup group-Searchable
0059     //!
0060     //! Specifically, this is equivalent to `contains`, except `in` takes its
0061     //! arguments in reverse order. Like `contains`, `in` can also be applied
0062     //! in infix notation for increased expressiveness. This function is not a
0063     //! method that can be overriden; it is just a convenience function
0064     //! provided with the concept.
0065     //!
0066     //!
0067     //! Example
0068     //! -------
0069     //! @include example/in.cpp
0070     BOOST_HANA_INLINE_VARIABLE constexpr auto in = hana::infix(hana::flip(hana::contains));
0071 }} // end namespace boost::hana
0072
0073 #endif // !BOOST_HANA_FWD_CONTAINS_HPP