How do you check if a key exists without creating it ?

exilepanda has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks,

use Data::Dumper;
$x = {};
1 if ( exists $x->{W} ) ;
1 if ( defined $x->{X} ) ;
1 if ( $x->{Y} ) ;
1 if ( exists $x->{Y}{X}  ) ;
1 if ( defined $x->{Z}{A}  );
print Dumper $x;
[download]

Result :

$VAR1 = {
          'Z' => {},
          'Y' => {}
        };
[download]

What I don't want is Z, Y create by itself, when I try to check if some keys from inner are existed or not. Can I do that ? Hopefully this won't be the only solution

if ( $x->{Y} ) {
  if ( $x->{Y}{Z} ) {
    1 if ( $x->{Y}{Z}{A} ) ;
  }
} ; # $VAR={};
[download]

Any clues? Thank you very much!

Comment on How do you check if a key exists without creating it ? Select or Download Code

Replies are listed 'Best First'.
Re: How do you check if a key exists without creating it ? by wind (Priest) on Oct 06, 2012 at 08:43 UTC
You're just falling into autovivification. Check for existence of the lower level first if you don't want it autocreated: `use Data::Dumper; $x = {}; 1 if ( $x->{Y} && exists $x->{Y}{X} ) ; 1 if ( $x->{Z} && defined $x->{Z}{A} ); print Dumper $x;` [download]	[reply] [d/l]
Re^2: How do you check if a key exists without creating it ? by exilepanda (Friar) on Oct 06, 2012 at 11:34 UTC
haha.. yes, lesson just learned! Thank you very much! =)	[reply]
Re: How do you check if a key exists without creating it ? by Anonymous Monk on Oct 06, 2012 at 08:44 UTC
Well, you start by not creating it :) no autovivification; `if( exists $foo->{bar}{anything}{you}{want} ){ }` [download] Or use Data::Diver 'Dive'; `if( my $want = Dive( $foo, qw/ bar anything you want / ) ){ ... }` [download]	[reply] [d/l] [select]
Re^2: How do you check if a key exists without creating it ? by exilepanda (Friar) on Oct 06, 2012 at 09:00 UTC
THANK YOU IT WORKS PERFECTLY!!! THANK YOU VERY MUCH!!! =D	[reply]


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