# object

$self={
hash_ref=>{item1=>'value1',item2=>'value2'}
}

# cmp funtion

sub byvalue
{

#instead of

$a<=>$b;

#something like

$self->{hash_ref}->{$a}<=>$self->{hash_ref}->{$b};

#how do I access $self in this function?

}

# object's sort function

sub sort_hash_ref_keys_by_value
{

my $self=shift;

my @keys=sort byvalue keys(%{$self->{hash_ref}});

}