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

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

@@ -0,0 +1,66 @@
+/*!
+@file
+Forward declares `boost::hana::drop_front`.
+
+@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_DROP_FRONT_HPP
+#define BOOST_HANA_FWD_DROP_FRONT_HPP
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/when.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! Drop the first `n` elements of an iterable, and return the rest.
+    //! @ingroup group-Iterable
+    //!
+    //! Given an `Iterable` `xs` with a linearization of `[x1, x2, ...]` and
+    //! a non-negative `IntegralConstant` `n`, `drop_front(xs, n)` is an
+    //! iterable with the same tag as `xs` whose linearization is
+    //! `[xn+1, xn+2, ...]`. In particular, note that this function does not
+    //! mutate the original iterable in any way. If `n` is not given, it
+    //! defaults to an `IntegralConstant` with a value equal to `1`.
+    //!
+    //! In case `length(xs) <= n`, `drop_front` will simply drop the whole
+    //! iterable without failing, thus returning an empty iterable. This is
+    //! different from `drop_front_exactly`, which expects `n <= length(xs)`
+    //! but can be better optimized because of this additional guarantee.
+    //!
+    //!
+    //! @param xs
+    //! The iterable from which elements are dropped.
+    //!
+    //! @param n
+    //! A non-negative `IntegralConstant` representing the number of elements
+    //! to be dropped from the iterable. If `n` is not given, it defaults to
+    //! an `IntegralConstant` with a value equal to `1`.
+    //!
+    //!
+    //! Example
+    //! -------
+    //! @include example/drop_front.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    constexpr auto drop_front = [](auto&& xs[, auto const& n]) {
+        return tag-dispatched;
+    };
+#else
+    template <typename It, typename = void>
+    struct drop_front_impl : drop_front_impl<It, when<true>> { };
+
+    struct drop_front_t {
+        template <typename Xs, typename N>
+        constexpr auto operator()(Xs&& xs, N const& n) const;
+
+        template <typename Xs>
+        constexpr auto operator()(Xs&& xs) const;
+    };
+
+    constexpr drop_front_t drop_front{};
+#endif
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FWD_DROP_FRONT_HPP