Hi,
I am not sure if this is possible. I have a case statement which
checks for a regular expression. For example:
case text
when /(abc)(.)/
when /(xyz)(.)/
end
In the above snippet how can I use the instance variables pre_match
and post_match? I tried calling these methods without any qualifiers
but I got a NoMethodError. Where does Ruby store the MatchData if the
matching is done in a case statement?
Thanks
-subbu
On May 3, 2008, at 10:05 AM, [email protected] wrote:
In the above snippet how can I use the instance variables pre_match
and post_match? I tried calling these methods without any qualifiers
but I got a NoMethodError. Where does Ruby store the MatchData if the
matching is done in a case statement?
$1, $2, etc.
On 03.05.2008 18:00, [email protected] wrote:
but I got a NoMethodError. Where does Ruby store the MatchData if the
matching is done in a case statement?
$ irb
irb(main):001:0> /b/ =~ “abc”
=> 1
irb(main):002:0> $`
=> “a”
irb(main):003:0> $’
=> “c”
irb(main):004:0> $~
=> #MatchData:0x7ff9eb54
irb(main):005:0> $~.to_a
=> [“b”]
irb(main):006:0> $~.pre_match
=> “a”
irb(main):007:0> $~.post_match
=> “c”
irb(main):008:0>
But why do you have groups in your regular expressions if you are not
interested in the content? Also “(.)*” seems a bit odd because it might
not yield what you expect:
irb(main):008:0> /a(.)*/ =~ “abcdef”
=> 0
irb(main):009:0> $1
=> “f”
IMHO it is generally a bad idea to use grouping in the way you do it
because it will capture a lot that you are not interested in. It seems
you might rather want “(.*)”.
Kind regards
robert
On May 4, 3:11 am, Robert K. [email protected] wrote:
In the above snippet how can I use the instance variables pre_match
=> “c”
But why do you have groups in your regular expressions if you are not
you might rather want “(.*)”.Kind regards
robert
Hey Robert,
In my guess /b/ =~ “abc” is what sets $~ variable. Since I am not
using that statement anywhere that variable is not set at all. Instead
I am doing the matching in a case statement. As a result I am not able
to do something like $~.pre_match. I am not fond of $1, $2, etc
variables. I feel comfortable using the instance variables pre_match
and post_match.
But you solved the first problem I was trying to solve 
I was using
(.)* instead of (.) and I couldn’t get what I wanted. (.) is what I
needed. Thanks so much for that. Now I can use $1, $2 at least if not
pre_match and post_match.
-subbu
2008/5/3 [email protected]:
Where does Ruby store the MatchData if the
matching is done in a case statement?
Subbu, there’s also Regexp.last_match. Sometimes this reads better
than those Perl-like variables.
Regards,
Pit
On May 4, 5:40 am, Pit C. [email protected] wrote:
2008/5/3 [email protected]:
Where does Ruby store the MatchData if the
matching is done in a case statement?Subbu, there’s also Regexp.last_match. Sometimes this reads better
than those Perl-like variables.Regards,
Pit
Hi Pitt,
I did use Regexp.last_match. But its a class method. I am interested
in using something like pre_match and post_match methods which are
instance variables. But looks like my code never created the instance
of MatchData.
Thanks
-subbu
On May 4, 2008, at 8:25 AM, [email protected] wrote:
Pit
Hi Pitt,
I did use Regexp.last_match. But its a class method. I am interested
in using something like pre_match and post_match methods which are
instance variables. But looks like my code never created the instance
of MatchData.
Regexp.last_match.pre_match
James Edward G. II
Hi –
On Sun, 4 May 2008, [email protected] wrote:
On May 4, 5:40 am, Pit C. [email protected] wrote:
2008/5/3 [email protected]:
Where does Ruby store the MatchData if the
matching is done in a case statement?
Matching doesn’t change in or out of a case statement; it’s still the
same thing.
instance variables. But looks like my code never created the instance
of MatchData.
Methods aren’t instance variables; they’re methods
Ruby keeps track of the last match operation performed, and that’s
what you get in $~ (which is a MatchData object) and some of the
Regexp class methods.
David
On 04.05.2008 15:21, [email protected] wrote:
and post_match? I tried calling these methods without any qualifiers
=> #MatchData:0x7ff9eb54
not yield what you expect:irb(main):008:0> /a(.)*/ =~ “abcdef”
=> 0
irb(main):009:0> $1
=> “f”IMHO it is generally a bad idea to use grouping in the way you do it
because it will capture a lot that you are not interested in. It seems
you might rather want “(.*)”.
In my guess /b/ =~ “abc” is what sets $~ variable. Since I am not
using that statement anywhere that variable is not set at all.
That’s complete nonsense. Did you try it out? I guess not. Come on,
don’t be so lazy.
Instead
I am doing the matching in a case statement. As a result I am not able
to do something like $~.pre_match. I am not fond of $1, $2, etc
variables. I feel comfortable using the instance variables pre_match
and post_match.
pre_match and post_match are not instance variables but methods of class
MatchData.
But you solved the first problem I was trying to solve
I was using
(.)* instead of (.) and I couldn’t get what I wanted. (.) is what I
needed. Thanks so much for that. Now I can use $1, $2 at least if not
pre_match and post_match.
irb(main):007:0> /b/ === “abc”
=> true
irb(main):008:0> $~
=> #MatchData:0x100230b8
irb(main):009:0> $~.pre_match
=> “a”
irb(main):010:0> $~.post_match
=> “c”
irb(main):011:0>
robert
Hi –
On Mon, 5 May 2008, Rick DeNatale wrote:
what you get in $~ (which is a MatchData object) and some of the
Regexp class methods.And $~ is actually a thread local global, so it holds the matchdata
produced by the last successful match on the current thread.I’m pretty sure that Regexp.last_match is thread-safe as well.
I believe it just returns $~, so it should be identical in terms of
thread safety.
David
On Sun, May 4, 2008 at 11:22 AM, David A. Black [email protected]
wrote:
2008/5/3 [email protected]:
Where does Ruby store the MatchData if the
matching is done in a case statement?Matching doesn’t change in or out of a case statement; it’s still the
same thing.
Ruby keeps track of the last match operation performed, and that’s
what you get in $~ (which is a MatchData object) and some of the
Regexp class methods.
And $~ is actually a thread local global, so it holds the matchdata
produced by the last successful match on the current thread.
I’m pretty sure that Regexp.last_match is thread-safe as well.
–
Rick DeNatale
My blog on Ruby
http://talklikeaduck.denhaven2.com/
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