Added thirdparty: boost library

thirdparty/include/boost/hana/front.hpp

@@ -0,0 +1,47 @@
+/*!
+@file
+Defines `boost::hana::front`.
+
+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_FRONT_HPP
+#define BOOST_HANA_FRONT_HPP
+
+#include <boost/hana/fwd/front.hpp>
+
+#include <boost/hana/at.hpp>
+#include <boost/hana/concept/iterable.hpp>
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/dispatch.hpp>
+
+
+namespace boost { namespace hana {
+    //! @cond
+    template <typename Xs>
+    constexpr decltype(auto) front_t::operator()(Xs&& xs) const {
+        using It = typename hana::tag_of<Xs>::type;
+        using Front = BOOST_HANA_DISPATCH_IF(front_impl<It>,
+            hana::Iterable<It>::value
+        );
+
+    #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
+        static_assert(hana::Iterable<It>::value,
+        "hana::front(xs) requires 'xs' to be an Iterable");
+    #endif
+
+        return Front::apply(static_cast<Xs&&>(xs));
+    }
+    //! @endcond
+
+    template <typename It, bool condition>
+    struct front_impl<It, when<condition>> : default_ {
+        template <typename Xs>
+        static constexpr decltype(auto) apply(Xs&& xs)
+        { return hana::at_c<0>(static_cast<Xs&&>(xs)); }
+    };
+}} // end namespace boost::hana
+
+#endif // !BOOST_HANA_FRONT_HPP