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diff --git a/boost/hana/if.hpp b/boost/hana/if.hpp
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+/*!
+@file
+Defines `boost::hana::if_`.
+
+@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_IF_HPP
+#define BOOST_HANA_IF_HPP
+
+#include <boost/hana/fwd/if.hpp>
+
+#include <boost/hana/concept/logical.hpp>
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/dispatch.hpp>
+#include <boost/hana/eval_if.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! @cond
+    template <typename Cond, typename Then, typename Else>
+    constexpr decltype(auto) if_t::operator()(Cond&& cond, Then&& then, Else&& else_) const {
+        using Bool = typename hana::tag_of<Cond>::type;
+        using If = BOOST_HANA_DISPATCH_IF(if_impl<Bool>,
+            hana::Logical<Bool>::value
+        );
+
+    #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
+        static_assert(hana::Logical<Bool>::value,
+        "hana::if_(cond, then, else) requires 'cond' to be a Logical");
+    #endif
+
+        return If::apply(static_cast<Cond&&>(cond),
+                         static_cast<Then&&>(then),
+                         static_cast<Else&&>(else_));
+    }
+    //! @endcond
+
+    namespace detail {
+        template <typename T>
+        struct hold {
+            T value;
+            constexpr T&& operator()() && { return static_cast<T&&>(value); }
+        };
+    }
+
+    template <typename L, bool condition>
+    struct if_impl<L, when<condition>> : default_ {
+        template <typename C, typename T, typename E>
+        static constexpr auto apply(C&& c, T&& t, E&& e) {
+            return hana::eval_if(static_cast<C&&>(c),
+                detail::hold<T&&>{static_cast<T&&>(t)},
+                detail::hold<E&&>{static_cast<E&&>(e)}
+            );
+        }
+    };
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_IF_HPP