Require Boost 1.58 or later

include/beast/core/consuming_buffers.hpp

@@ -9,6 +9,7 @@
 #define BEAST_CONSUMING_BUFFERS_HPP
 
 #include <beast/config.hpp>
+#include <beast/core/detail/in_place_init.hpp>
 #include <boost/asio/buffer.hpp>
 #include <boost/optional.hpp>
 #include <cstdint>

include/beast/core/detail/in_place_init.hpp

@@ -0,0 +1,40 @@
+//
+// Copyright (c) 2013-2017 Vinnie Falco (vinnie dot falco at gmail dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef BEAST_DETAIL_IN_PLACE_INIT_HPP
+#define BEAST_DETAIL_IN_PLACE_INIT_HPP
+
+#include <boost/version.hpp>
+
+// Provide boost::in_place_init_t and boost::in_place_init
+// for Boost versions earlier than 1.63.0.
+
+#if BOOST_VERSION < 106300
+
+namespace boost {
+
+namespace optional_ns {
+ 
+// a tag for in-place initialization of contained value
+struct in_place_init_t
+{
+  struct init_tag{};
+  explicit in_place_init_t(init_tag){}
+};            
+const in_place_init_t in_place_init ((in_place_init_t::init_tag()));
+  
+} // namespace optional_ns
+
+using optional_ns::in_place_init_t;
+using optional_ns::in_place_init;
+
+}
+
+#endif
+
+#endif
+