hana/fwd/less.hpp

0001 /*!
0002 @file
0003 Forward declares `boost::hana::less`.
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_LESS_HPP
0011 #define BOOST_HANA_FWD_LESS_HPP
0012
0013 #include <boost/hana/config.hpp>
0014 #include <boost/hana/core/when.hpp>
0015 #include <boost/hana/detail/nested_than_fwd.hpp>
0016
0017
0018 namespace boost { namespace hana {
0019     //! Returns a `Logical` representing whether `x` is less than `y`.
0020     //! @ingroup group-Orderable
0021     //!
0022     //!
0023     //! Signature
0024     //! ---------
0025     //! Given a Logical `Bool` and two Orderables `A` and `B` with a common
0026     //! embedding, the signature is
0027     //! @f$ \mathrm{less} : A \times B \to Bool @f$.
0028     //!
0029     //! @param x, y
0030     //! Two objects to compare.
0031     //!
0032     //!
0033     //! Example
0034     //! -------
0035     //! @include example/less.cpp
0036 #ifdef BOOST_HANA_DOXYGEN_INVOKED
0037     constexpr auto less = [](auto&& x, auto&& y) {
0038         return tag-dispatched;
0039     };
0040 #else
0041     template <typename T, typename U, typename = void>
0042     struct less_impl : less_impl<T, U, when<true>> { };
0043
0044     struct less_t : detail::nested_than<less_t> {
0045         template <typename X, typename Y>
0046         constexpr auto operator()(X&& x, Y&& y) const;
0047     };
0048
0049     BOOST_HANA_INLINE_VARIABLE constexpr less_t less{};
0050 #endif
0051 }} // end namespace boost::hana
0052
0053 #endif // !BOOST_HANA_FWD_LESS_HPP