[Boost-users] [xpressive] Using placeholder in semantic actions

Subject: [Boost-users] [xpressive] Using placeholder in semantic actions
From: Symons, Greg - SSD (Greg.Symons_at_[hidden])
Date: 2008-09-04 11:13:36

Hi!

I'm trying to use xpressive with semantic actions that use a placeholder, but I
can't quite see the right way to do it. Here's my code:

namespace grammar
{
   using namespace boost::xpressive;

   struct ParsedUri
   {
      std::string hostname;
      std::string modelPath;
      std::string diagramPath;
   };

   static placeholder<ParsedUri> result;

   static const mark_tag model(1), diagram(2), host(1);
   static const char          pathSep        = '/';

   static sregex              unreserved     =
                                 set
                                 [
                                    alpha |
                                    digit |
                                    '-'   |
                                    '.'   |
                                    '_'   |
                                    '~'   |
                                    ' '   |
                                    ':'   |
                                    '$'
                                 ];
   static sregex              pctEncoded     =
                                 as_xpr('%') >> xdigit >> xdigit;
   static sregex              pathElem       =
                                 *(unreserved | pctEncoded);
   static sregex              path           =
                                 pathElem |
                                 *(pathElem >> pathSep >> by_ref(path));
   static sregex              drive          =
                                 alpha >> ':';
   static sregex              quad           =
                                 repeat<1,3>(digit)
                                 [ check(as<int>(_) >= 1 && as<int>(_) <= 255) ];
   static sregex              ipv4           =
                                 repeat<3>(quad >> '.') >> quad;
   static sregex              hostname       = !(ipv4 | pathElem);
   static sregex              pathNoHost     =
                                 pathSep >> drive >> pathSep >> path;
   static sregex              pathHost       =
                                 (host= hostname) >> pathSep >> path
                                 [ result.hostname = host ];
   static sregex              modelPath      = pathNoHost | pathHost
   static sregex              uri            =
                                 "rosert://" >> (model= modelPath) >> '?' >> (diagram= path)
                                 [ result.modelPath = model, result.diagramPath = diagram ];
}

What happens is that when I compile the code, I get a compile error for the
lines accessing the placeholder saying that the various members of the structure
are not members of placeholder<T>, which looking at regex_actions.hpp seems to
make sense to me. But in the example using placeholder<T> in the docs, it looks
like you can use it in the semantic action as if it were a T. Somewhere I'm
misunderstanding something, and I don't know what. Can anyone help me here?

--
Gregory Symons
Software Engineer
ITT Space Systems Division
greg.symons_at_[hidden]
[phone]
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