stabilize build system: depends, installer, boost/bdb fixes, cross targets groundwork

depends/x86_64-pc-linux-gnu/include/boost/hana/fwd/symmetric_difference.hpp

@@ -0,0 +1,54 @@
+/*!
+@file
+Forward declares `boost::hana::symmetric_difference`.
+
+@copyright Louis Dionne 2013-2017
+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>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! Returns the symmetric set-theoretic difference of two sets.
+    //! @relates hana::set
+    //!
+    //! Given two sets `xs` and `ys`, `symmetric_difference(xs, ys)` is a new
+    //! set containing all the elements of `xs` that are not contained in `ys`,
+    //! and all the elements of `ys` that are not contained in `xs`. The
+    //! symmetric difference of two sets satisfies the following:
+    //! @code
+    //!     symmetric_difference(xs, ys) == union_(difference(xs, ys), difference(ys, xs))
+    //! @endcode
+    //!
+    //!
+    //! @param xs, ys
+    //! Two sets to compute the symmetric difference of.
+    //!
+    //!
+    //! Example
+    //! -------
+    //! @include example/symmetric_difference.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    constexpr auto symmetric_difference = [](auto&& xs, auto&& ys) {
+        return tag-dispatched;
+    };
+#else
+    template <typename S, typename = void>
+    struct symmetric_difference_impl : symmetric_difference_impl<S, when<true>> { };
+
+    struct symmetric_difference_t {
+        template <typename Xs, typename Ys>
+        constexpr auto operator()(Xs&& xs, Ys&& ys) const;
+    };
+
+    constexpr symmetric_difference_t symmetric_difference{};
+#endif
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FWD_SYMMETRIC_DIFFERENCE_HPP