Data Encapsulation in Perl?

Question

Hello Perl community on SO. I am using Perl since a few years, but since I am following SO, I recognized that I know Perl not enough.

I wrote I quite big script over the past 4 years and tried to do this in OO style. I know that Perl<6 is not really OO.

So one point I don't like is that I have no data encapsulation, that means no Variables that are really private to a package ("class") (or maybe I don't know how to do it).

I have something like this (only a small part of my script)

package TAG;

sub new () {
    my $classname = shift;
    my $self      = {};

    bless( $self, $classname );
    $self->initialize();
    return $self;
}

sub initialize() {
    my $self = shift;

    # Only an example, I have a long list of items in this "class"
    $self->{ID}          = "NA"; 
}

sub setID() {
    ...
}

sub getID() {
    ...
}

In my main script I am using it then this way:

my $CurrentItem;
$CurrentItem = new TAG();

$CurrentItem->getID()

but

$CurrentItem->{ID} = "Something";

is also working, but I would prefer, that this is not possible.

Is there a way to get a better encapsulation of the data I am using in the "class", so that I am (or other users are) forced to use the get and set methods?

Answer 1

This is an issue that's been discussed in several places, and there are several possible work-arounds, but none of them are necessarily ideal.

This paper discusses options such as closures, scalars, and a limited access hash using Tie::SecureHash, preferring the last approach.

This blog argues that in perl there are times when encapsulation should be violated, although the comments bring up some negatives for doing so.

You can also look into moose for your Perl 5 objects. It's written to encourage the use of encapsulated objects.