1 files changed, 48 insertions, 0 deletions
diff --git a/boost/hana/duplicate.hpp b/boost/hana/duplicate.hpp
new file mode 100644
index 0000000000..1df6fb7a85
--- /dev/null
+++ b/boost/hana/duplicate.hpp
@@ -0,0 +1,48 @@
+/*!
+@file
+Defines `boost::hana::duplicate`.
+
+@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_DUPLICATE_HPP
+#define BOOST_HANA_DUPLICATE_HPP
+
+#include <boost/hana/fwd/duplicate.hpp>
+
+#include <boost/hana/concept/comonad.hpp>
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/dispatch.hpp>
+#include <boost/hana/extend.hpp>
+#include <boost/hana/functional/id.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! @cond
+    template <typename W_>
+    constexpr decltype(auto) duplicate_t::operator()(W_&& w) const {
+        using W = typename hana::tag_of<W_>::type;
+        using Duplicate = BOOST_HANA_DISPATCH_IF(duplicate_impl<W>,
+            hana::Comonad<W>::value
+        );
+
+    #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
+        static_assert(hana::Comonad<W>::value,
+        "hana::duplicate(w) requires 'w' to be a Comonad");
+    #endif
+
+        return Duplicate::apply(static_cast<W_&&>(w));
+    }
+    //! @endcond
+
+    template <typename W, bool condition>
+    struct duplicate_impl<W, when<condition>> : default_ {
+        template <typename X>
+        static constexpr decltype(auto) apply(X&& x)
+        { return hana::extend(static_cast<X&&>(x), hana::id); }
+    };
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_DUPLICATE_HPP