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( #3333=superdoc: print w/replies, xml ) Need Help??
> 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/ $VAR1 = [ 1, undef, 2, 3 ]; $VAR1 = [ 'b', 'a', 'c' ]; $VAR1 = [ 1, 2, 3 ]; $VAR1 = [ 'a', 'x', 'c', 'b' ]; 1 at d:/tmp/pm/ 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

In reply to Re^2: unexpected modify hash in a distance with grep { $_ } by LanX
in thread unexpected modify hash in a distance with grep { $_ } by leszekdubiel

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