update boost

linx64/include/boost/url/grammar/impl/optional_rule.hpp

@@ -0,0 +1,42 @@
+//
+// Copyright (c) 2016-2019 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)
+//
+// Official repository: https://github.com/boostorg/url
+//
+
+#ifndef BOOST_URL_GRAMMAR_IMPL_OPTIONAL_RULE_HPP
+#define BOOST_URL_GRAMMAR_IMPL_OPTIONAL_RULE_HPP
+
+#include <boost/url/grammar/error.hpp>
+
+namespace boost {
+namespace urls {
+namespace grammar {
+
+template<class R>
+auto
+optional_rule_t<R>::
+parse(
+    char const*& it,
+    char const* end) const ->
+        system::result<value_type>
+{
+    if(it == end)
+        return boost::none;
+    auto const it0 = it;
+    auto rv =
+        this->get().parse(it, end);
+    if(rv)
+        return value_type(*rv);
+    it = it0;
+    return boost::none;
+}
+
+} // grammar
+} // urls
+} // boost
+
+#endif