Added thirdparty: boost library

thirdparty/include/boost/hana/fwd/symmetric_difference.hpp

@@ -0,0 +1,32 @@
+/*!
+@file
+Forward declares `boost::hana::symmetric_difference`.
+
+Copyright Louis Dionne 2013-2022
+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_SYMMETRIC_DIFFERENCE_HPP
+#define BOOST_HANA_FWD_SYMMETRIC_DIFFERENCE_HPP
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/when.hpp>
+
+
+namespace boost { namespace hana {
+    // Note: This function is documented per datatype/concept only.
+    //! @cond
+    template <typename S, typename = void>
+    struct symmetric_difference_impl : symmetric_difference_impl<S, when<true>> { };
+    //! @endcond
+
+    struct symmetric_difference_t {
+        template <typename Xs, typename Ys>
+        constexpr auto operator()(Xs&&, Ys&&) const;
+    };
+
+    BOOST_HANA_INLINE_VARIABLE constexpr symmetric_difference_t symmetric_difference{};
+}} // end namespace boost::hana
+
+#endif // !BOOST_HANA_FWD_SYMMETRIC_DIFFERENCE_HPP