hana/fwd/for_each.hpp

0001 /*!
0002 @file
0003 Forward declares `boost::hana::for_each`.
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_FOR_EACH_HPP
0011 #define BOOST_HANA_FWD_FOR_EACH_HPP
0012
0013 #include <boost/hana/config.hpp>
0014 #include <boost/hana/core/when.hpp>
0015
0016
0017 namespace boost { namespace hana {
0018     //! Perform an action on each element of a foldable, discarding
0019     //! the result each time.
0020     //! @ingroup group-Foldable
0021     //!
0022     //! Iteration is done from left to right, i.e. in the same order as when
0023     //! using `fold_left`. If the structure is not finite, this method will
0024     //! not terminate.
0025     //!
0026     //!
0027     //! @param xs
0028     //! The structure to iterate over.
0029     //!
0030     //! @param f
0031     //! A function called as `f(x)` for each element `x` of the structure.
0032     //! The result of `f(x)`, whatever it is, is ignored.
0033     //!
0034     //!
0035     //! Example
0036     //! -------
0037     //! @include example/for_each.cpp
0038 #ifdef BOOST_HANA_DOXYGEN_INVOKED
0039     constexpr auto for_each = [](auto&& xs, auto&& f) -> void {
0040         tag-dispatched;
0041     };
0042 #else
0043     template <typename T, typename = void>
0044     struct for_each_impl : for_each_impl<T, when<true>> { };
0045
0046     struct for_each_t {
0047         template <typename Xs, typename F>
0048         constexpr void operator()(Xs&& xs, F&& f) const;
0049     };
0050
0051     BOOST_HANA_INLINE_VARIABLE constexpr for_each_t for_each{};
0052 #endif
0053 }} // end namespace boost::hana
0054
0055 #endif // !BOOST_HANA_FWD_FOR_EACH_HPP