Perl : Get the keys of a blessed hashref

Question

There are 2 packages in the code.

Package 1 :

package Foo;
sub new {
    my ($class, $args) = @_;
    my $hashref = {'a' => 1, 'b' => 2};
    bless ($self, $class);
    return $self;
}

Package 2 :

package Fuz;
use Foo;
.
.
.
.
my $obj = Foo->new($args);

How to get the keys of the blessed hashref in the object ?

Am aware of Acme::Damn and Data::Structure::Util modules in perl to unbless the object. Are there any other ways to achieve this ?

Answer 1

Blessing a hash ref does not change that it is still a hash ref. You can therefore dereference it as usual:

my @keys = keys %$obj;

Answer 2

First, you should use strict and use warnings, because that code doesn't compile as it is. What is $self on line 5? You never define it. Modifying the package code to this:

package Foo;
use strict;
use warnings;
sub new {
    my ($class, $args) = @_;
    my $hashref = {'a' => 1, 'b' => 2};
    bless ($args, $class);
    return $args;
}
1;

Now this will compile, but what do you want to do with $hashref? Are you expecting parameters passed in via $args or can $hashref replace $args? Assuming that $args really isn't needed, let's use this for Foo:

package Foo;
use strict;
use warnings;
sub new {
    my ($class) = @_;
    my $hashref = {'a' => 1, 'b' => 2};
    bless ($hashref, $class);
    return $hashref;
}
1;

Now, when you call new, you'll be returned a blessed hashref that you can get the keys from:

> perl -d -Ilib -e '1'

Loading DB routines from perl5db.pl version 1.33
Editor support available.

Enter h or `h h' for help, or `perldoc perldebug' for more help.

main::(-e:1):   1
  DB<1> use Foo

  DB<2> $obj = Foo->new()

  DB<3> x $obj
0  Foo=HASH(0x2a16374)
   'a' => 1
   'b' => 2
  DB<4> x keys(%{$obj})
0  'a'
1  'b'
  DB<5>

Answer 3

You can still use keys on the $obj

my $obj = Foo->new($args);
my @k = keys %$obj;