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Re^2: unexpected modify hash in a distance with grep { $_ }

by LanX (Cardinal)
on Dec 20, 2019 at 18:19 UTC ( #11110442=note: print w/replies, xml ) Need Help??


in reply to Re: unexpected modify hash in a distance with grep { $_ }
in thread unexpected modify hash in a distance with grep { $_ }

> Not a problem with grep. $$h{x} is autovivified before grep happens.

Nope, it happens because of the aliasing of the hash value inside grep, but I'm not sure how.

#!/usr/bin/perl use strict; use warnings; use Data::Dumper; my $h = { 'a' => 1, 'b' => 2, 'c' => 3, }; warn Dumper [ $$h{a}, $$h{x}, $$h{b}, $$h{c} ]; warn Dumper [ keys %$h ]; warn Dumper [ grep {$_} $$h{a}, $$h{x}, $$h{b}, $$h{c} ]; warn Dumper [ keys %$h ]; warn !$$h{y}; warn Dumper [ keys %$h ];

C:/Perl_524/bin\perl.exe d:/tmp/pm/grep_autovivify.pl $VAR1 = [ 1, undef, 2, 3 ]; $VAR1 = [ 'b', 'a', 'c' ]; $VAR1 = [ 1, 2, 3 ]; $VAR1 = [ 'a', 'x', 'c', 'b' ]; 1 at d:/tmp/pm/grep_autovivify.pl line 19. $VAR1 = [ 'a', 'x', 'c', 'b' ];

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

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Re^3: unexpected modify hash in a distance with grep { $_ }
by afoken (Canon) on Dec 20, 2019 at 21:06 UTC
    Nope, it happens because of the aliasing of the hash value inside grep, but I'm not sure how.

    Interesting effect. I see your output with plain perl v5.22.2 (from 2016) on Linux x86-64 and with Strawberry v5.14.2 (from 2011) on Windows 64 bit. So this seems to be an old, unsolved problem.

    Alexander

    --
    Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)
      Maybe I should file a bug on that? I will report bug for Debian...
        I think yes, you can do this. But link to this thread.

        Me personally I'd wait the weekend, monks tend to find related tickets or route causes pretty fast.

        But that's a philosophical question, probably p5p rather prefers closing multiple reports.

        Cheers Rolf
        (addicted to the Perl Programming Language :)
        Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

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