Re: Named capture backreferences cannot be used in character classes?

G'day BrowserUk,

You can use a postponed subexpression replacing [^\k<FQ>]+ with (??{"[^$+{FQ}]+"}). It's flagged as "experimental" - that may affect your choice to use it. Here's my test:

#!/usr/bin/env perl

use 5.010;
use strict;
use warnings;

my @test_strings = qw{""" "'" '"' ''' ""' "'' '"" ''"};

my $re = qr{ (?<FQ>"|') (??{ "[^$+{FQ}]+" }) \k<FQ> }x;

for (@test_strings) {
    say "Testing [$_] : ", (/$re/ ? '' : 'no '), 'match.';
}
[download]

Output:

$ pm_re_kname_in_charclass.pl
Testing ["""] : no match.
Testing ["'"] : match.
Testing ['"'] : match.
Testing ['''] : no match.
Testing [""'] : no match.
Testing ["''] : no match.
Testing ['""] : no match.
Testing [''"] : no match.
[download]

-- Ken

Comment on Re: Named capture backreferences cannot be used in character classes? Select or Download Code

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Re^2: Named capture backreferences cannot be used in character classes? by BrowserUk (Patriarch) on Sep 27, 2013 at 06:01 UTC
You can use a postponed subexpression replacing It's flagged as "experimental" - that may affect your choice to use it. That would certainly work -- and I don't have a problem with it being "experimental"; as far as I have observed it hasn't changed in all the years it has been there and I'm already having to where I need recursive regex -- but I prefer to avoid it if there is a less performance sapping alternative. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply]
Re^3: Named capture backreferences cannot be used in character classes? by yitzchak (Sexton) on Sep 30, 2013 at 03:06 UTC
They changed at one point; IIRC it used to be something like `(?p{...})`; I think Ilya originally envisioned it as a limited scope version of a hypothetical `qr/foo$bar/p` that would at match time use the current value of `$bar`.	[reply] [d/l] [select]
Re^4: Named capture backreferences cannot be used in character classes? ( (?p{ code }) became by Anonymous Monk on Sep 30, 2013 at 07:05 UTC
It was renamed to perlre/(??{ code }) in Fri, 3 Mar 2000 02:19:50 +0000 (02:19 +0000) http://perl5.git.perl.org/perl.git/commit/14455d6cc193f1e4316f87b9dbe258db24ceb714 and finaly removed in http://search.cpan.org/dist/perl/pod/perl5100delta.pod#%28?p{}%29_has_been_removed	[reply]
Re^4: Named capture backreferences cannot be used in character classes? by BrowserUk (Patriarch) on Sep 30, 2013 at 08:45 UTC
Thanks for the information. According to anonymonks addendum, this all pre-dates my first use of Perl which started just a couple of weeks before I found this place in June, 2002. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply]
Re^3: Named capture backreferences cannot be used in character classes? by kcott (Archbishop) on Sep 27, 2013 at 13:09 UTC
"... I don't have a problem with it being "experimental"; as far as I have observed it hasn't changed in all the years it has been there ..." When I read that this afternoon, that was my understanding too. However, poking aroung in perl5180delta some hours later (on a completely unrelated matter), I found: "/(?{})/ and /(??{})/ have been heavily reworked". That's really just an FYI, if you're interested. It's still marked "experimental" and I saw nothing to indicate any specific performance enhancements. -- Ken	[reply]
Re^4: Named capture backreferences cannot be used in character classes? by BrowserUk (Patriarch) on Sep 27, 2013 at 13:43 UTC
That's really just an FYI, Thanks for the heads up. I haven't moved onto 5.18 yet, but I will be doing so soon. Thankfully, my primary use of the feature is where I have regex elements that are codependent. EG. `A => qr[...${B()}...], B => qr[...${C()}...], C => qr[...${A()}...],` [download] Which doesn't work because there is no way to order them such that all dependancies can be resolved at compile-time. Instead I have to use: `A => qr[...(??{B()})...], B => qr[...(??{C()})...], C => qr[...(??{A()})...],` [download] Which doesn't seem to be affected by the changes. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l] [select]