hana/fwd/intersperse.hpp

0001 /*!
0002 @file
0003 Forward declares `boost::hana::intersperse`.
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_INTERSPERSE_HPP
0011 #define BOOST_HANA_FWD_INTERSPERSE_HPP
0012
0013 #include <boost/hana/config.hpp>
0014 #include <boost/hana/core/when.hpp>
0015
0016
0017 namespace boost { namespace hana {
0018     //! Insert a value between each pair of elements in a finite sequence.
0019     //! @ingroup group-Sequence
0020     //!
0021     //! Given a finite `Sequence` `xs` with a linearization of
0022     //! `[x1, x2, ..., xn]`, `intersperse(xs, z)` is a new sequence with a
0023     //! linearization of `[x1, z, x2, z, x3, ..., xn-1, z, xn]`. In other
0024     //! words, it inserts the `z` element between every pair of elements of
0025     //! the original sequence. If the sequence is empty or has a single
0026     //! element, `intersperse` returns the sequence as-is. In all cases,
0027     //! the sequence must be finite.
0028     //!
0029     //!
0030     //! @param xs
0031     //! The sequence in which a value is interspersed.
0032     //!
0033     //! @param z
0034     //! The value to be inserted between every pair of elements of the sequence.
0035     //!
0036     //!
0037     //! Example
0038     //! -------
0039     //! @include example/intersperse.cpp
0040 #ifdef BOOST_HANA_DOXYGEN_INVOKED
0041     constexpr auto intersperse = [](auto&& xs, auto&& z) {
0042         return tag-dispatched;
0043     };
0044 #else
0045     template <typename S, typename = void>
0046     struct intersperse_impl : intersperse_impl<S, when<true>> { };
0047
0048     struct intersperse_t {
0049         template <typename Xs, typename Z>
0050         constexpr auto operator()(Xs&& xs, Z&& z) const;
0051     };
0052
0053     BOOST_HANA_INLINE_VARIABLE constexpr intersperse_t intersperse{};
0054 #endif
0055 }} // end namespace boost::hana
0056
0057 #endif // !BOOST_HANA_FWD_INTERSPERSE_HPP