Dear monks,

I came across this behaviour in perl which I find unintuitive, was wondering what the use case scenario for it is or whether I have done something wrong to bring it about...

I had a statement checking for the existence of data like so return 0 unless keys %{$hashref->{$key}} and I failed to realise that $key may not always exist.

I would have expected to see an error if $href->{$key} is undefined and therefore not a reference, but instead $key was just added to the hash.

Example:

#!/usr/bin/perl -w

#perl-5.22.3

use strict;

my $href = {
            cat => {milk => 1},
            dog => {bone => 1}
};

if (keys %{$href->{cow}}) {
    print "noop\n";
} else {
    if (exists $href->{cow}) {
        print "holy cow\n";
    } else {
        print "no cow\n";
    }
}

[download]

This prints 'holy cow'

In reply to keys %{$hash->{$href}} adds $href to the hash if it doesnt exist? by nikmit

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