Re^6: On the regex pattern variable to be inserted into another (which recompile???)

Well, I take it back, and have updated my answers.

Perl does special-case /$foo/g and s/$foo/.../g to avoid re-compiling. It does not optimize changing the anchor like /\G$foo/gc, which is the actual code from my module.

The testing I did at the time was based on performance, rather than specifically tracing whether the compilation got invoked. It could be that evaling a coderef with the expanded regex text still performs better than referencing a compiled regex, but but I don't really have time right now to go back and benchmark it.

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Re^7: On the regex pattern variable to be inserted into another (which recompile???) by hv (Prior) on Feb 11, 2022 at 18:59 UTC
AFAIR Perl caches the previous stringification of the regexp, and compares that against the stringification of the new pattern to determine whether it needs recompiling. The stringification of a compiled pattern always captures those outside flags that affect compile-time so as to make this (and interpolation) safe, that's why you see for example: `% perl -E 'say qr{foo}i' (?^ui:foo) %` [download] The `/g` flag is not listed in the docs because it is not supported by `qr{}`: `% perl -E 'say qr{foo}g' Unknown regexp modifier "/g" at -e line 1, near "say " Execution of -e aborted due to compilation errors. %` [download] (I think that error message could probably be improved. Patches welcome. :)	[reply] [d/l] [select]

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Re^7: On the regex pattern variable to be inserted into another (which recompile???)
by hv (Prior) on Feb 11, 2022 at 18:59 UTC

AFAIR Perl caches the previous stringification of the regexp, and compares that against the stringification of the new pattern to determine whether it needs recompiling. The stringification of a compiled pattern always captures those outside flags that affect compile-time so as to make this (and interpolation) safe, that's why you see for example:

% perl -E 'say qr{foo}i'
(?^ui:foo)
%
[download]

The /g flag is not listed in the docs because it is not supported by qr{}:

% perl -E 'say qr{foo}g'
Unknown regexp modifier "/g" at -e line 1, near "say "
Execution of -e aborted due to compilation errors.
%
[download]

(I think that error message could probably be improved. Patches welcome. :)

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