added x3 example of wrapping multiple attributes using std::tuple

example/x3/Jamfile

@@ -61,3 +61,5 @@ exe x3_calc9 :
     calc/calc9/statement.cpp
     calc/calc9/main.cpp
 ;
+
+exe x3_tuple : attributes/tuple.cpp ;

example/x3/attributes/tuple.cpp

@@ -0,0 +1,51 @@
+
+/*=============================================================================
+    Copyright (c) 2019 Tom Tan
+
+    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)
+=============================================================================*/
+#include <boost/config/warning_disable.hpp>
+#include <boost/spirit/home/x3.hpp>
+
+#include <boost/fusion/adapted/std_tuple.hpp>
+
+#include <iostream>
+#include <tuple>
+#include <string>
+
+//
+// X3 does not support more than one attribute anymore in the parse function,
+// this example show how to wrap multiple attributes into one leveraging std::tuple.
+//
+
+std::tuple<uint32_t, uint32_t, uint32_t> parse_message_prefix_revision(const std::string &s)
+{
+
+  namespace x3 = boost::spirit::x3;
+
+  auto const uint_3_digits = x3::uint_parser<std::uint32_t, 10, 3, 3>{};
+  auto const uint_4_digits = x3::uint_parser<std::uint32_t, 10, 4, 4>{};
+
+  auto iter = s.cbegin();
+  auto end_iter = s.cend();
+
+  std::tuple<uint32_t, uint32_t, uint32_t> length_id_revision;
+
+  x3::parse(iter, end_iter,
+            uint_4_digits >> uint_4_digits >> uint_3_digits,
+            length_id_revision);
+
+  return length_id_revision;
+}
+
+int main()
+{
+  std::string s = "00200060001";
+
+  std::cout << "parsing " << s << '\n';
+  auto [len, id, rev] = parse_message_prefix_revision(s);
+  std::cout << "length = " << len << '\n'
+            << "id = " << id << '\n'
+            << "revision =" << rev;
+}