Re^15: Reusing a complex regexp in multiple spots, escaping the regexp

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Re^16: Reusing a complex regexp in multiple spots, escaping the regexp by LanX (Saint) on Apr 17, 2026 at 13:59 UTC
> on unthreaded, once. I tried your code on "unthreaded" perl and it prints twice. It seems like this weird "interpolation" ° resolves to `"x1" =~ /x1/` which doesn't make much sense as a bug demo. I don't understand how this is proving anything??? Cheers Rolf _{(addicted to the Perl Programming Language :) see Wikisyntax for the Monastery} °) seems like you are dereferencing a ref to the literal number `1` `DB<1> say "${\1}" 1` [download] you probably meant a the regex back-reference to the first match `\1` ? But there is no first match ... ehm???	[reply] [d/l] [select]
Re^17: Reusing a complex regexp in multiple spots, escaping the regexp by dave_the_m (Monsignor) on Apr 17, 2026 at 14:52 UTC
I tried your code on "unthreaded" perl and it prints twice. It seems like this weird "interpolation" ° resolves to "x1" =~ /x1/ which doesn't make much sense as a bug demo. On a perl interpreter compiled without threads support it prints "doing arg" once; on a threaded perl interpreter it prints twice - see the example run below. The match itself works correctly in both cases: it resolves to /x1/. My example was to show that there are strange side-effects which depend on the particlar perl interpreter you run it under. There are other edge case effects, the details of which I can't recall off the top of my head. `$ perl5420 -v This is perl 5, version 42, subversion 0 (v5.42.0) built for x86_64-li +nux $ perl5420 ~/tmp/p doing arg match match $ perl5420t -v This is perl 5, version 42, subversion 0 (v5.42.0) built for x86_64-li +nux-thread-multi $ perl5420t ~/tmp/p doing arg match doing arg match $` [download] Dave.	[reply] [d/l]
Re^18: Reusing a complex regexp in multiple spots, escaping the regexp by LanX (Saint) on Apr 17, 2026 at 15:13 UTC
Thanks for the clarification. ° Honestly, when injecting code evaluation into a variable interpolation, I'm not surprised to get inconsistent side effects. It would be of bigger concern if it also happened with more "official" means like `(?{...})` or `(??{...})` Cheers Rolf _{(addicted to the Perl Programming Language :) see Wikisyntax for the Monastery} °) how popular are Perl builds without thread support?	[reply] [d/l] [select]
Re^19: Reusing a complex regexp in multiple spots, escaping the regexp by dave_the_m (Monsignor) on Apr 17, 2026 at 15:29 UTC
Re^20: Reusing a complex regexp in multiple spots, escaping the regexp by LanX (Saint) on Apr 17, 2026 at 17:07 UTC
Re^16: Reusing a complex regexp in multiple spots, escaping the regexp by LanX (Saint) on Apr 17, 2026 at 13:27 UTC
Thanks! Please, how can I reproduce this? There are multiple threaded Perl models. I never wrote threaded Perlš, so please explain What's the output without /o then? And as follow ups How does this qualify as a bug and not a feature? Is `state` better in this respect? ° Shouldn't this be documented as side effect, (at least with a footnote)? Cheers Rolf _{(addicted to the Perl Programming Language :) see Wikisyntax for the Monastery} Footnotes °) updated š) I suppose only a tiny minority ever did.	[reply]
Re^17: Reusing a complex regexp in multiple spots, escaping the regexp by choroba (Cardinal) on Apr 17, 2026 at 13:30 UTC
I think "threaded perl" means an interpreter compiled with -Dusethreads. It changes the output regardless of whether you use threads in the code or not. `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l]

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