hana/fwd/cartesian_product.hpp

0001 /*!
0002 @file
0003 Forward declares `boost::hana::cartesian_product`.
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_CARTESIAN_PRODUCT_HPP
0011 #define BOOST_HANA_FWD_CARTESIAN_PRODUCT_HPP
0012
0013 #include <boost/hana/config.hpp>
0014 #include <boost/hana/core/when.hpp>
0015
0016
0017 namespace boost { namespace hana {
0018     //! Computes the cartesian product of a sequence of sequences.
0019     //! @ingroup group-Sequence
0020     //!
0021     //! Given a sequence of sequences, `cartesian_product` returns a new
0022     //! sequence of sequences containing the cartesian product of the
0023     //! original sequences. For this method to finish, a finite number
0024     //! of finite sequences must be provided.
0025     //!
0026     //! @note
0027     //! All the sequences must have the same tag, and that tag must also match
0028     //! that of the top-level sequence.
0029     //!
0030     //!
0031     //! Signature
0032     //! ---------
0033     //! Given a `Sequence` `S(T)`, the signature is
0034     //! \f[
0035     //!     \mathtt{cartesian\_product} : S(S(T)) \to S(S(T))
0036     //! \f]
0037     //!
0038     //! @param xs
0039     //! A sequence of sequences of which the cartesian product is computed.
0040     //!
0041     //!
0042     //! Example
0043     //! -------
0044     //! @include example/cartesian_product.cpp
0045 #ifdef BOOST_HANA_DOXYGEN_INVOKED
0046     constexpr auto cartesian_product = [](auto&& xs) {
0047         return tag-dispatched;
0048     };
0049 #else
0050     template <typename S, typename = void>
0051     struct cartesian_product_impl : cartesian_product_impl<S, when<true>> { };
0052
0053     struct cartesian_product_t {
0054         template <typename Xs>
0055         constexpr auto operator()(Xs&& xs) const;
0056     };
0057
0058     BOOST_HANA_INLINE_VARIABLE constexpr cartesian_product_t cartesian_product{};
0059 #endif
0060 }} // end namespace boost::hana
0061
0062 #endif // !BOOST_HANA_FWD_CARTESIAN_PRODUCT_HPP