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

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

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+/*!
+@file
+Forward declares `boost::hana::span`.
+
+@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_SPAN_HPP
+#define BOOST_HANA_FWD_SPAN_HPP
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/when.hpp>
+#include <boost/hana/detail/nested_by_fwd.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! Returns a `Product` containing the longest prefix of a sequence
+    //! satisfying a predicate, and the rest of the sequence.
+    //! @ingroup group-Sequence
+    //!
+    //! The first component of the returned `Product` is a sequence for which
+    //! all elements satisfy the given predicate. The second component of the
+    //! returned `Product` is a sequence containing the remainder of the
+    //! argument. Both or either sequences may be empty, depending on the
+    //! input argument. More specifically,
+    //! @code
+    //!     span(xs, predicate) == make_pair(take_while(xs, predicate),
+    //!                                      drop_while(xs, predicate))
+    //! @endcode
+    //! except that `make_pair` may be an arbitrary `Product`.
+    //!
+    //!
+    //! Signature
+    //! ---------
+    //! Given a `Sequence` `S(T)`, a `Logical` `Bool` and a predicate
+    //! \f$ T \to Bool \f$, `span` has the following signature:
+    //! \f[
+    //!     \mathtt{span} : S(T) \times (T \to Bool) \to S(T) \times S(T)
+    //! \f]
+    //!
+    //! @param xs
+    //! The sequence to break into two parts.
+    //!
+    //! @param predicate
+    //! A function called as `predicate(x)`, where `x` is an element of the
+    //! sequence, and returning a `Logical. In the current implementation of
+    //! the library, `predicate` has to return a compile-time `Logical`.
+    //!
+    //!
+    //! Syntactic sugar (`span.by`)
+    //! ---------------------------
+    //! `span` can be called in an alternate way, which provides a nice syntax
+    //! in some cases where the predicate is short:
+    //! @code
+    //!     span.by(predicate, xs) == span(xs, predicate)
+    //!     span.by(predicate) == span(-, predicate)
+    //! @endcode
+    //!
+    //! where `span(-, predicate)` denotes the partial application of
+    //! `span` to `predicate`.
+    //!
+    //!
+    //! Example
+    //! -------
+    //! @include example/span.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    constexpr auto span = [](auto&& xs, auto&& predicate) {
+        return tag-dispatched;
+    };
+#else
+    template <typename S, typename = void>
+    struct span_impl : span_impl<S, when<true>> { };
+
+    struct span_t : detail::nested_by<span_t> {
+        template <typename Xs, typename Pred>
+        constexpr auto operator()(Xs&& xs, Pred&& pred) const;
+    };
+
+    constexpr span_t span{};
+#endif
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FWD_SPAN_HPP