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/*!
@file
Defines `boost::hana::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_PRODUCT_HPP
#define BOOST_HANA_PRODUCT_HPP
#include <boost/hana/fwd/product.hpp>
#include <boost/hana/concept/foldable.hpp>
#include <boost/hana/concept/ring.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/fold_left.hpp>
#include <boost/hana/integral_constant.hpp> // required by fwd decl
#include <boost/hana/mult.hpp>
#include <boost/hana/one.hpp>
BOOST_HANA_NAMESPACE_BEGIN
template <typename R>
struct product_t {
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Ring<R>::value,
"hana::product<R> requires 'R' to be a Ring");
#endif
template <typename Xs>
constexpr decltype(auto) operator()(Xs&& xs) const {
using S = typename hana::tag_of<Xs>::type;
using Product = BOOST_HANA_DISPATCH_IF(product_impl<S>,
hana::Foldable<S>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Foldable<S>::value,
"hana::product<R>(xs) requires 'xs' to be Foldable");
#endif
return Product::template apply<R>(static_cast<Xs&&>(xs));
}
};
template <typename T, bool condition>
struct product_impl<T, when<condition>> : default_ {
template <typename R, typename Xs>
static constexpr decltype(auto) apply(Xs&& xs) {
return hana::fold_left(static_cast<Xs&&>(xs), hana::one<R>(), hana::mult);
}
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_PRODUCT_HPP
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