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

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

@@ -0,0 +1,57 @@
+/*!
+@file
+Forward declares `boost::hana::duplicate`.
+
+@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_DUPLICATE_HPP
+#define BOOST_HANA_FWD_DUPLICATE_HPP
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/when.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! Add an extra layer of comonadic context to a comonadic value.
+    //! @ingroup group-Comonad
+    //!
+    //! Given a value already in a comonadic context, `duplicate` wraps this
+    //! value with an additional layer of comonadic context. This can be seen
+    //! as the dual operation to `flatten` from the Monad concept.
+    //!
+    //!
+    //! Signature
+    //! ---------
+    //! Given a Comonad `W`, the signature is
+    //! \f$
+    //!     \mathtt{duplicate} : W(T) \to W(W(T))
+    //! \f$
+    //!
+    //! @param w
+    //! The value to wrap in an additional level of comonadic context.
+    //!
+    //!
+    //! Example
+    //! -------
+    //! @include example/duplicate.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    constexpr auto duplicate = [](auto&& w) -> decltype(auto) {
+        return tag-dispatched;
+    };
+#else
+    template <typename W, typename = void>
+    struct duplicate_impl : duplicate_impl<W, when<true>> { };
+
+    struct duplicate_t {
+        template <typename W_>
+        constexpr decltype(auto) operator()(W_&& w) const;
+    };
+
+    constexpr duplicate_t duplicate{};
+#endif
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FWD_DUPLICATE_HPP