Imported Upstream version 1.61.0

Change-Id: I96a1f878d1e6164f01e9aadd5147f38fca448d90
Signed-off-by: DongHun Kwak <dh0128.kwak@samsung.com>

1 files changed, 67 insertions, 0 deletions

diff --git a/boost/hana/fwd/minus.hpp b/boost/hana/fwd/minus.hpp
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+/*!
+@file
+Forward declares `boost::hana::minus`.
+
+@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_MINUS_HPP
+#define BOOST_HANA_FWD_MINUS_HPP
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/when.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! Subtract two elements of a group.
+    //! @ingroup group-Group
+    //!
+    //! Specifically, this performs the `Monoid` operation on the first
+    //! argument and on the inverse of the second argument, thus being
+    //! equivalent to:
+    //! @code
+    //!     minus(x, y) == plus(x, negate(y))
+    //! @endcode
+    //!
+    //!
+    //! Cross-type version of the method
+    //! --------------------------------
+    //! The `minus` method is "overloaded" to handle distinct data types
+    //! with certain properties. Specifically, `minus` is defined for
+    //! _distinct_ data types `A` and `B` such that
+    //! 1. `A` and `B` share a common data type `C`, as determined by the
+    //!    `common` metafunction
+    //! 2. `A`, `B` and `C` are all `Group`s when taken individually
+    //! 3. `to<C> : A -> B` and `to<C> : B -> C` are `Group`-embeddings, as
+    //!    determined by the `is_embedding` metafunction.
+    //!
+    //! The definition of `minus` for data types satisfying the above
+    //! properties is obtained by setting
+    //! @code
+    //!     minus(x, y) = minus(to<C>(x), to<C>(y))
+    //! @endcode
+    //!
+    //!
+    //! Example
+    //! -------
+    //! @include example/minus.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    constexpr auto minus = [](auto&& x, auto&& y) -> decltype(auto) {
+        return tag-dispatched;
+    };
+#else
+    template <typename T, typename U, typename = void>
+    struct minus_impl : minus_impl<T, U, when<true>> { };
+
+    struct minus_t {
+        template <typename X, typename Y>
+        constexpr decltype(auto) operator()(X&& x, Y&& y) const;
+    };
+
+    constexpr minus_t minus{};
+#endif
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FWD_MINUS_HPP