Maintaining Contained Object Attributes

giulienk has asked for the wisdom of the Perl Monks concerning the following question:

Once again here is the new version of my new() method.

sub new {
    my ($self, $tn, $key, $value);
    my $class = shift;
    if ($_[2] =~ /^\d+$/) { # this suppose no %hash key is all numeric
        $tn = Telephone::Number->new(shift, shift, shift);
    } else {
        $tn = Telephone::Number->new(shift);
    }
    my ($smstext, %hash) = @_;
        $self = bless {
            'tn' => $tn,
            'smstext' => $smstext,
            'cookie_jar' => exists $hash{cookie_jar} ? 
                            delete $hash{cookie_jar} : 
                            "lwpcookies.txt",
        }, $class;
        @{$self}{keys %{$tn}} = @{$tn}{keys %{$tn}};
        @{$self}{keys %hash} = @hash{keys %hash}; #dragonchild suggest
+ion
    $self;
}
[download]

Now i have created a new Telephone::Number object (temporary namespace) cause i need it to do some dirty work parsing phone numbers... but this is not the point.
With the line @{$self}{keys %{$tn}} = @{$tn}{keys %{$tn}}; i got a copy of the values of $self->{tn} in $self, but that's not what i want. I'd like to have in %{$self} aliases to the hash variables in %{$self->{tn}} so that when i change $self->{some_key_from_tn} i change also $self->{tn}->{some_key_from_tn}
I hope i explained what i need, maybe just a bit confused.
Thanks for advice.
Giulio

Edit kudra, 2001-10-30 Changed title

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Re: Once again looking for Wisdom by davorg (Chancellor) on Oct 30, 2001 at 15:00 UTC
Sounds a bit like you're trying to break encapsulation - which is probably a bad thing. Given that all access to the values in `$self` will be via accessor functions (or, at least, they should be) why not let the accessor functions deal with keeping the two values in step. `sub some_key_from_tn { my $self = shift; if (@_) { # called to set value $self->{some_key_from_tn} = $_[0]; # call Telephone::Number method to set value $self->{tn}->some_key_from_tn($_[0]); } $self->{some_key_from_tn}; }` [download] -- <http://www.dave.org.uk> "The first rule of Perl club is you don't talk about Perl club."	[reply] [d/l]
Re: Maintaining Contained Object Attributes by Fletch (Bishop) on Oct 30, 2001 at 17:02 UTC
Following up davorg's advice about always going through accesors, you could look into Class::Delegation or Class::Delegate to have those accessors automagically forwarded to be called on contained objects.	[reply]
(tye)Re: Maintaining Contained Object Attributes by tye (Sage) on Oct 30, 2001 at 20:22 UTC
Well, you can use: `@{$self}{keys %{$tn}}= \( @{$tn}{keys %{$tn}} );` and then changing `${$self->{some_key_from_tn}}` will also change `$self->{tn}->{some_key_from_tn}`. This can be nice if you have a generic accessor methods (perhaps autoloaded) that could just check if the value is a scalar reference and set/get the referenced scalar in such cases. Although the guts of Perl support having two hash values be aliases of each other (AFAICT), the language doesn't provide a way of achieving that (AFAICT). So I suppose you could write some XS code to do what you want. So you might be better off doing what davorg suggested. However, even if I went with the accessor route, I'd just have the "fetch" part get the attribute from the contained object rather than keeping two copies in sync. - tye (but my friends call me "Tye")	[reply] [d/l] [select]