From: Tom Pollard <tomp@...>
Date: 2007-02-04T06:59:56+09:00
Subject: Re: Named groups in regexp matches?


On Feb 3, 2007, at 11:23 AM, Robert Dober wrote:
> What I do might be enough for your purpose
>
> S=Struct.new(:key, :value)
> => S
> irb(main):002:0>  r=%r{(\w+)\s*=\s*(.*)}
> => /(\w+)\s*=\s*(.*)/
> irb(main):003:0> m= r.match("name = Tom Pollard")
> => #<MatchData:0xb7dfbb5c>
> irb(main):004:0> s=S.new(*m.captures)
> => #<struct S key="name", value="Tom Pollard">
> irb(main):005:0> s.key
> => "name"
> irb(main):006:0>  s.value
> => "Tom Pollard"
>
> this could easily be wrapped into a class BTW.

Thanks.  That's not a bad idea, but it only addresses half of my  
problem, because I still need to be careful to use non-capturing  
groups for the things I don't want to capture.  In Python, I can  
ignore that - labeling the groups I /do/ want to capture is enough.   
Here are a few examples from my Python code:

WIND_RE = re.compile(r"""^(?P<dir>[\dO]{3}|[0O]|///|MMM|VRB)
                           (?P<speed>P?[\dO]{2,3}|[0O]+|[/M]{2,3})
                         (G(?P<gust>P?(\d{1,3}|[/M]{1,3})))?
                           (?P<units>KTS?|LT|K|T|KMH|MPS)?
                       (\s+(?P<varfrom>\d\d\d)V
                           (?P<varto>\d\d\d))?\s+""",
                           re.VERBOSE)
VISIBILITY_RE =   re.compile(r"""^(?P<vis>(?P<dist>M?(\d\s+)?\d/\d\d?| 
M?\d+)
                                      ( \s*(?P<units>SM|KM|M|U) |
                                           (?P<dir>[NSEW][EW]?) )? |
                                    CAVOK )\s+""",
                                    re.VERBOSE)
RUNWAY_RE = re.compile(r"""^(RVRNO |
                              R(?P<name>\d\d(RR?|LL?|C)?)/
                               (?P<low>(M|P)?\d\d\d\d)
                             (V(?P<high>(M|P)?\d\d\d\d))?
                               (?P<unit>FT)?[/NDU]*)\s+""",
                               re.VERBOSE)
TEMP_RE = re.compile(r"""^(?P<temp>(M|-)?\d+|//|XX|MM)/
                           (?P<dewpt>(M|-)?\d+|//|XX|MM)?\s+""",
                           re.VERBOSE)

To port these to pre-1.9 Ruby, I'll need to remove the '?P<name>'  
labels and change the other groups from '(...)' to '(?:...)'.  Once  
I've done that I can worry about assigning labels to the captured  
groups, after they're matched, or just using the index captures.   
There's nothing about that that's not straightforward; I'm mostly  
struggling with my motivation for going through this effort at all,  
simply to port a working, well-debugged and fairly fast Python module  
to Ruby, especially since I'm fairly sure the resulting Ruby module  
will be much slower and harder to maintain.

Tom