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+/*!
+@file
+Forward declares `boost::hana::cartesian_product`.
+
+@copyright Louis Dionne 2013-2016
+Distributed under the Boost Software License, Version 1.0.
+(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+ */
+
+#ifndef BOOST_HANA_FWD_CARTESIAN_PRODUCT_HPP
+#define BOOST_HANA_FWD_CARTESIAN_PRODUCT_HPP
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/when.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+ //! Computes the cartesian product of a sequence of sequences.
+ //! @ingroup group-Sequence
+ //!
+ //! Given a sequence of sequences, `cartesian_product` returns a new
+ //! sequence of sequences containing the cartesian product of the
+ //! original sequences. For this method to finish, a finite number
+ //! of finite sequences must be provided.
+ //!
+ //! @note
+ //! All the sequences must have the same tag, and that tag must also match
+ //! that of the top-level sequence.
+ //!
+ //!
+ //! Signature
+ //! ---------
+ //! Given a `Sequence` `S(T)`, the signature is
+ //! \f[
+ //! \mathtt{cartesian\_product} : S(S(T)) \to S(S(T))
+ //! \f]
+ //!
+ //! @param xs
+ //! A sequence of sequences of which the cartesian product is computed.
+ //!
+ //!
+ //! Example
+ //! -------
+ //! @include example/cartesian_product.cpp
+ //!
+ //!
+ //! Benchmarks
+ //! ----------
+ //! <div class="benchmark-chart"
+ //! style="min-width: 310px; height: 400px; margin: 0 auto"
+ //! data-dataset="benchmark.cartesian_product.compile.json">
+ //! </div>
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+ constexpr auto cartesian_product = [](auto&& xs) {
+ return tag-dispatched;
+ };
+#else
+ template <typename S, typename = void>
+ struct cartesian_product_impl : cartesian_product_impl<S, when<true>> { };
+
+ struct cartesian_product_t {
+ template <typename Xs>
+ constexpr auto operator()(Xs&& xs) const;
+ };
+
+ constexpr cartesian_product_t cartesian_product{};
+#endif
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FWD_CARTESIAN_PRODUCT_HPP