hana/fwd/accessors.hpp

0001 /*!
0002 @file
0003 Forward declares `boost::hana::accessors`.
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_ACCESSORS_HPP
0011 #define BOOST_HANA_FWD_ACCESSORS_HPP
0012
0013 #include <boost/hana/config.hpp>
0014 #include <boost/hana/core/when.hpp>
0015
0016
0017 namespace boost { namespace hana {
0018     //! Returns a `Sequence` of pairs representing the accessors of the
0019     //! data structure.
0020     //! @ingroup group-Struct
0021     //!
0022     //! Given a `Struct` `S`, `accessors<S>()` is a `Sequence` of `Product`s
0023     //! where the first element of each pair is the "name" of a member of
0024     //! the `Struct`, and the second element of each pair is a function that
0025     //! can be used to access that member when given an object of the proper
0026     //! data type. As described in the global documentation for `Struct`, the
0027     //! accessor functions in this sequence must be move-independent.
0028     //!
0029     //!
0030     //! Example
0031     //! -------
0032     //! @include example/accessors.cpp
0033 #ifdef BOOST_HANA_DOXYGEN_INVOKED
0034     template <typename S>
0035     constexpr auto accessors = []() {
0036         return tag-dispatched;
0037     };
0038 #else
0039     template <typename S, typename = void>
0040     struct accessors_impl : accessors_impl<S, when<true>> { };
0041
0042     template <typename S>
0043     struct accessors_t;
0044
0045     template <typename S>
0046     BOOST_HANA_INLINE_VARIABLE constexpr accessors_t<S> accessors{};
0047 #endif
0048 }} // end namespace boost::hana
0049
0050 #endif // !BOOST_HANA_FWD_ACCESSORS_HPP