Moose's attribute vs simple sub?

Question

How to decide - what is the recommended way for the next code fragment?

I have a Moose-based module, where some data is a simple HashRef.

It is possible to write - as a Mooseish HashRef, like:

package Some;
has 'data' => (
        isa => 'HashRef',
        builder => '_build_href',
        init_arg => undef,
        lazy => 1,
);

sub _build-href {
        my $href;
        $href = { a=>'a', b=>'b'}; #some code what builds a href
        return $href;
}

vs

sub  data {
        my $href;
        $href = { a=>'a', b=>'b'}; #some code what builds a href
        return $href;
}

What is the difference? I'm asking because when calling:

my $obj = Some->new;
my $href = $obj->data;

In both case I get a correct HashRef. So when is it recommended to use a Moose-ish has construction (which is longer) vs a simple data sub?

PS: probably this question is so simple for an average perl programmer, but please, keep in mind, I'm still only learning perl.

Answer 1

If you have an attribute, then whoever is constructing the object can set the hashref in the constructor:

my $obj = Some->new(data => { a => 'c', b => 'd' });

(Though in your example, you've used init_arg => undef which would disable that ability.)

Also, in the case of the attribute, the builder is only run once per object while with a standard method, the method might be called multiple times. If building the hashref is "expensive", that may be an important concern.

Another difference you'll notice is with this:

use Data::Dumper;
my $obj  = Some->new;
$obj->data->{c} = 123;
print Dumper( $obj->data );