1 files changed, 58 insertions, 0 deletions
diff --git a/boost/hana/product.hpp b/boost/hana/product.hpp
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+++ b/boost/hana/product.hpp
@@ -0,0 +1,58 @@
+/*!
+@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