hana/fwd/replace.hpp

0001 /*!
0002 @file
0003 Forward declares `boost::hana::replace`.
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_REPLACE_HPP
0011 #define BOOST_HANA_FWD_REPLACE_HPP
0012
0013 #include <boost/hana/config.hpp>
0014 #include <boost/hana/core/when.hpp>
0015
0016
0017 namespace boost { namespace hana {
0018     //! Replace all the elements of a structure that compare equal
0019     //! to some `value` with some new fixed value.
0020     //! @ingroup group-Functor
0021     //!
0022     //!
0023     //! Signature
0024     //! ---------
0025     //! Given `F` a Functor and `U` a type that can be compared with `T`,
0026     //! the signature is
0027     //! \f$
0028     //!     \mathtt{replace} : F(T) \times U \times T \to F(T)
0029     //! \f$
0030     //!
0031     //! @param xs
0032     //! The structure to replace elements of.
0033     //!
0034     //! @param oldval
0035     //! An object compared with each element of the structure. Elements
0036     //! of the structure that compare equal to `oldval` are replaced
0037     //! by `newval` in the new structure.
0038     //!
0039     //! @param newval
0040     //! A value by which every element `x` of the structure that compares
0041     //! equal to `oldval` is replaced.
0042     //!
0043     //!
0044     //! Example
0045     //! -------
0046     //! @include example/replace.cpp
0047 #ifdef BOOST_HANA_DOXYGEN_INVOKED
0048     constexpr auto replace = [](auto&& xs, auto&& oldval, auto&& newval) {
0049         return tag-dispatched;
0050     };
0051 #else
0052     template <typename Xs, typename = void>
0053     struct replace_impl : replace_impl<Xs, when<true>> { };
0054
0055     struct replace_t {
0056         template <typename Xs, typename OldVal, typename NewVal>
0057         constexpr auto operator()(Xs&& xs, OldVal&& oldval, NewVal&& newval) const;
0058     };
0059
0060     BOOST_HANA_INLINE_VARIABLE constexpr replace_t replace{};
0061 #endif
0062 }} // end namespace boost::hana
0063
0064 #endif // !BOOST_HANA_FWD_REPLACE_HPP