Re^14: Reusing a complex regexp in multiple spots, escaping the regexp

> The longest explanation of /o

This covers exactly my understanding.

You'll also find this in perlop for m//

- "But now, the only reasons to use /o are one of:..."

The perldocs are vast and often redundant, and sometimes contradictory.

They are like much of the code base a collaborative design.

The wording at perlre is at best dubious and as far as I can see not substationated.

As long as nobody shows me a real bug caused by /o I'd call this BS.

Cheers Rolf
_{(addicted to the Perl Programming Language :)

see Wikisyntax for the Monastery}

Comment on Re^14: Reusing a complex regexp in multiple spots, escaping the regexp

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Re^15: Reusing a complex regexp in multiple spots, escaping the regexp by dave_the_m (Monsignor) on Apr 17, 2026 at 11:52 UTC
Well for example, consider the following code: `for my $i (1..2) { print "match\n" if "x1" =~ /x${print "doing arg\n"; \1}/o; }` [download] On threaded perls it prints "doing arg" twice; on unthreaded, once. Dave.	[reply] [d/l]
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 $` [download] Dave.	[reply] [d/l]
Re^18: Reusing a complex regexp in multiple spots, escaping the regexp by LanX (Saint) on Apr 17, 2026 at 15:13 UTC
Re^19: Reusing a complex regexp in multiple spots, escaping the regexp by dave_the_m (Monsignor) on Apr 17, 2026 at 15:29 UTC
Some notes below your chosen depth have not been shown here
Re^16: Reusing a complex regexp in multiple spots, escaping the regexp by LanX (Saint) on Apr 17, 2026 at 13:27 UTC
Thanks! Please, how can I reproduce this? There are multiple threaded Perl models. I never wrote threaded Perlš, so please explain What's the output without /o then? And as follow ups How does this qualify as a bug and not a feature? Is `state` better in this respect? ° Shouldn't this be documented as side effect, (at least with a footnote)? Cheers Rolf _{(addicted to the Perl Programming Language :) see Wikisyntax for the Monastery} Footnotes °) updated š) I suppose only a tiny minority ever did.	[reply]
Re^17: Reusing a complex regexp in multiple spots, escaping the regexp by choroba (Cardinal) on Apr 17, 2026 at 13:30 UTC
I think "threaded perl" means an interpreter compiled with -Dusethreads. It changes the output regardless of whether you use threads in the code or not. `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^ARGV,3]`	[reply] [d/l]

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