hana/fwd/transform.hpp

0001 /*!
0002 @file
0003 Forward declares `boost::hana::transform`.
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_TRANSFORM_HPP
0011 #define BOOST_HANA_FWD_TRANSFORM_HPP
0012
0013 #include <boost/hana/config.hpp>
0014 #include <boost/hana/core/when.hpp>
0015
0016
0017 namespace boost { namespace hana {
0018     //! Map a function over a `Functor`.
0019     //! @ingroup group-Functor
0020     //!
0021     //!
0022     //! Signature
0023     //! ---------
0024     //! Given `F` a Functor, the signature is
0025     //! \f$
0026     //!     \mathtt{transform} : F(T) \times (T \to U) \to F(U)
0027     //! \f$
0028     //!
0029     //! @param xs
0030     //! The structure to map `f` over.
0031     //!
0032     //! @param f
0033     //! A function called as `f(x)` on element(s) `x` of the structure,
0034     //! and returning a new value to replace `x` in the structure.
0035     //!
0036     //!
0037     //! Example
0038     //! -------
0039     //! @include example/transform.cpp
0040 #ifdef BOOST_HANA_DOXYGEN_INVOKED
0041     constexpr auto transform = [](auto&& xs, auto&& f) {
0042         return tag-dispatched;
0043     };
0044 #else
0045     template <typename Xs, typename = void>
0046     struct transform_impl : transform_impl<Xs, when<true>> { };
0047
0048     struct transform_t {
0049         template <typename Xs, typename F>
0050         constexpr auto operator()(Xs&& xs, F&& f) const;
0051     };
0052
0053     BOOST_HANA_INLINE_VARIABLE constexpr transform_t transform{};
0054 #endif
0055 }} // end namespace boost::hana
0056
0057 #endif // !BOOST_HANA_FWD_TRANSFORM_HPP