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Subroutine arguments as aliases (was: Benchmarking a 'no-snails'world (was: Re: PSC #049 2022-01-07))

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Ed Avis
January 21, 2022 23:58
Subroutine arguments as aliases (was: Benchmarking a 'no-snails'world (was: Re: PSC #049 2022-01-07))
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On the subject of passing aliases to subroutines, I will note there is a longstanding wart with passing regexp capture variables.

     our $CONFIG = 'logging level 5';

    sub foo {
        if ($CONFIG =~ /logging level (\d+)/) { say "set logging to $1" }
        say "string is $_[0]";

    $_ = 'hello';
    /(.+)/ or die;

The contents of @_ get unexpectedly changed by what looks like a read-only regexp operation on some other variable.  This gotcha does lead to bugs in real code.  I think it would be better for perl to take a copy of $1, etc, when passing them to subroutines, rather than passing an alias.  After all, that's the behaviour we expect for other magic variables like $_.

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