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Re^2: ${^POSTMATCH} problem

by LanX (Sage)
on Jun 14, 2020 at 14:12 UTC ( #11118054=note: print w/replies, xml ) Need Help??

in reply to Re: ${^POSTMATCH} problem
in thread ${^POSTMATCH} problem

Good catch!

> It has nothing specifically to do with POSTMATCH,

I think the crucial point is that a $variable is passed by reference (read alias)


DB<25> sub tt { print "@_"} DB<26> tt ( ($foo = 1) , ($foo = 2) , ($foo = 3) ) 3 3 3 DB<27>

So the implementation of concat was changed in a function way...

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery

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Re^3: ${^POSTMATCH} problem
by ikegami (Pope) on Jun 14, 2020 at 15:34 UTC

    Yeah, The behaviour of ($foo = 1) . ($foo = 2) . ($foo = 3) used to be roughly equivalent to

    my $x = ""; $x .= ( $foo = 1 ); $x .= ( $foo = 2 ); $x .= ( $foo = 3 );

    But now, it's roughly equivalent to

    my $x = join("", ( $foo = 1 ), ( $foo = 2 ), ( $foo = 3 ), );

    In both cases, $foo itself is being put on the stack. The difference is when it's used (before it has a chance to be changed by later assignments, or after).

      I'm not happy about the behaviour of join here, because there is no way how CORE::join() will ever assign to the lvalue.

      So it should act like handling copies.

      I'm aware that we can override built-ins like join, so accessing the alias should still be possible. Theoretically that is.


      On second thought, a general new Warning in case of side effects of altered repeated variables as arguments may be more effective.

      Cheers Rolf
      (addicted to the Perl Programming Language :)
      Wikisyntax for the Monastery

        Short of *completely* rewriting Perl, it would have to make an actual copy to act like it was handling copies.

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