provide boost::mp11::mp_flatten if boost is too old

include/llama/Meta.hpp

@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#pragma once
+
+#include <boost/mp11.hpp>
+
+#if BOOST_MP11_VERSION < 107300
+//  Copyright 2015 Peter Dimov.
+//
+//  Distributed under the Boost Software License, Version 1.0.
+//
+// Boost Software License - Version 1.0 - August 17th, 2003
+//
+// Permission is hereby granted, free of charge, to any person or organization
+// obtaining a copy of the software and accompanying documentation covered by
+// this license (the "Software") to use, reproduce, display, distribute,
+// execute, and transmit the Software, and to prepare derivative works of the
+// Software, and to permit third-parties to whom the Software is furnished to
+// do so, all subject to the following:
+//
+// The copyright notices in the Software and this entire statement, including
+// the above license grant, this restriction and the following disclaimer,
+// must be included in all copies of the Software, in whole or in part, and
+// all derivative works of the Software, unless such copies or derivative
+// works are solely in the form of machine-executable object code generated by
+// a source language processor.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
+// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
+// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
+// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+namespace boost::mp11
+{
+    namespace detail
+    {
+        template <class L2>
+        struct mp_flatten_impl
+        {
+            template <class T>
+            using fn = mp_if<mp_similar<L2, T>, T, mp_list<T>>;
+        };
+    } // namespace detail
+
+    template <class L, class L2 = mp_clear<L>>
+    using mp_flatten = mp_apply<mp_append, mp_push_front<mp_transform_q<detail::mp_flatten_impl<L2>, L>, mp_clear<L>>>;
+} // namespace boost::mp11
+#endif

include/llama/llama.hpp

@@ -35,6 +35,7 @@
 #include "BlobAllocators.hpp"
 #include "Copy.hpp"
 #include "Core.hpp"
+#include "Meta.hpp"
 #include "Vector.hpp"
 #include "View.hpp"
 #include "VirtualRecord.hpp"