2. Is there a way to access the regex_id of the regex to which a semantic action belongs from the semantic action? More generally, can a semantic action be written as a custom function object that takes as argument some sort of environment (perhaps a match_results<>)?
<snip>
The action does not receive the match_results. The only way to get data into and out of an action is the way described in the docs. You will have to use xpressive::value, xpressive::reference or xpressive::placeholder to hold either the regex_id, a reference to the regex_id, or a promise to return a regex_id respectively. You can use those within the action.
All of these require providing the regex_id *manually*. <snip>
Right.
What I would like to do is this:
sregex rx = xpr[cout << _regex_id_]; // _regex_id_ is a special symbol
smatch what; // no need to provide anything here! _regex_id_ will be replaced by the // regex_id of rx regex_match(str, what, rx);
The reason this is important is because the action may be attached to a subregex of the regex on which the match is being done. For example:
placeholder
_regex_id; sregex sub = xpr[cout << _regex_id]; sregex rx = sub >> another_xpr; smatch what; what.let(_regex_id = ???); // sub.regex_id() needs to go here, but this // code knows only about rx, not about sub! regex_match(str, what, rx);
Is there no way to accomplish this?
Not at present, no. I don't think it would be hard to add. Could you file a feature request?
I filed https://svn.boost.org/trac/boost/ticket/7197 . Thanks, Nate