Question

I sometimes access a hash like this:

if(exists $ids{$name}){
    $id = $ids{$name};
}

Is that good practice? I’m a bit concerned that it contains two lookups where really one should be done. Is there a better way to check the existence and assign the value?

Answer 1

By checking with exists, you prevent autovivification. See Autovivification : What is it and why do I care?.

UPDATE: As trendels points out below, autovivification does not come into play in the example you posted. I am assuming that the actual code involves multi-level hashes.

Here is an illustration:

#!/usr/bin/perl

use strict;
use warnings;

use Data::Dumper;

my (%hash, $x);

if ( exists $hash{test}->{vivify} ) {
    $x = $hash{test}->{vivify}->{now};
}

print Dumper \%hash;

$x = $hash{test}->{vivify}->{now};

print Dumper \%hash;

__END__


C:\Temp> t
$VAR1 = {
    'test' => {}
};
$VAR1 = {
    'test' => {
        'vivify' => {}
    }
};