> MD> One of Uri's suggestions in RFC 158 was to compute $& only for
> MD> regexes that have a /k modifier. This would solve the $& problem
> MD> because Perl would compute $& only when asked to, and not for
> MD> every other regex in the rest of the program.
>
> the rfc was about making $& private to the block with the regex and
> only make the copy if /k is used or you use grabbing.
Making $& local to a block is not going to get a performance
improvement. The reason $1 is block localized is for safety, not
speed. Consider:
/(...)/;
foo();
print $1;
You might have had to worry that foo() would reset $1 somehow. But
because $1 is block-localized, you can be sure that it will be
restored automatically when foo() returns.
The performance gain in your RFC comes from the /k option, regardless
of whether or not $& gets block scope.
> a side question i have is whether this extra copy is a runtime effect or
> compile time. i would imagine runtime with some global flag being
> checked to see if $& is being used. so you could run fast and later load
> a module uses $& which slows you down.
That doesn't make any sense. Your proposal says that $& is only set
for regexes that have /k. Loading a module won't change your non-/k
regexes.
> in any case, i think we have a fair agreement on rfc 158 and i will
> freeze it if there is no further comments on it.
Please add a section that addresses Perl 5 -> Perl 6 translation
issues that will apply if your proposal is adopted.
