Why does the following gives the following output? $a1 is defined...

package A1;
use Hash::Merge;
use Data::Dumper;
  
sub new 
{
    my $class = shift;
    my $self =
    {
        length => 2,
    };
    return bless $self, $class;
}

1;


my $a1 = A1->new();
print("a1 = " . ref($a1) . "\n");

my %a = {'1' => $a1};

my $a3 = \%a;
print( Dumper($a3));

output:

a1 = A1
$VAR1 = {
          'HASH(0x247c568)' => undef
        };

I would've expected for the value to be a 'A1(0x...)' and not just undefined...

CodePudding user response：

The curly braces introduce a hash reference, but %a is a hash, not a reference. Therefore, the reference was stringified and used as the key, and there was nothing to use as the value, so it remained undefined.

Try

my %a = (1 => $a1);

instead.

You can also create the reference directly without %a:

my $a3 = {'1' => $a1};

You should always use warnings;. Perl would've told you

Reference found where even-sized list expected at ...