in reply to exists on hash autovivifies right?

Yes, it will autovivify intermediate structures (tested with 5.8.8 and 5.10) but not the final element being tested: 
use Data::Dumper;
my $x;
if (exists $x->{a}->{c}) {
  print "c exists\n";
} else {
  print "c doesn't exists\n";
}
print Dumper($x);
__END__
c doesn't exist
$VAR1 = {
          'a' => {}
        };

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Update: added confirmation about 5.10

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Re^2: exists on hash autovivifies right?
by ikegami (Patriarch) on Jun 29, 2008 at 07:11 UTC

    No, not really. exists never autovivifies, but it doesn't prevent anything else (such as ->) from causing autovivification. In the given example ($x->{a}->{c}), the first -> autovivifies $x and the second -> autovivifies $x->{a}. This occurs independently of exists. 

    >perl -le"$x->{a}->{c}; print $x; print $x->{a}"
HASH(0x225f18)
HASH(0x226020)

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      this is the best answer I read so far. thanks.
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Re^2: exists on hash autovivifies right?
by pc88mxer (Vicar) on Jun 28, 2008 at 23:24 UTC
    If you need to test for existence without autovivification, you'll have to code up a test that goes something like this: 
    sub my_exists {
  my $struct = shift;
  while (@_) {
    my $key = shift(@_);
    return false unless exists $hash->{$key};
    $hash = $hash->{$key};
  }
  1;
}

my $x = {};
if (my_exists($x, 'a', 'c')) {
  print "c exists\n";
} else {
  print "c doesn't exist\n";
}
print Dumper($x);

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        nice modu;es. thanks.
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      nice solution. thanks.
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Re^2: exists on hash autovivifies right?
by Anonymous Monk on Jun 28, 2008 at 23:11 UTC
    cool!
[reply]
      well, cool that you answered. btu I dislike the behavior a lot. who does not?
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