If you find yourself doing lots of "classical" Perl OO (with blessed hashes or arrays), you may want to take a look at Class::Struct. It provides a simple, but somewhat limited, way of producing your attribute methods. The nice things about Class::Struct are: it is a core module, and it is easy to understand.

If you really want to do OO with all the goodies, all the cool kids are using Moose. I haven't tried it in a project myself, but many people who I respect are using it with good success.

You can easily check to see if an argument is supplied to your setter methods:

use Carp qw(croak);

sub set_colour {
    my $this = shift

    croak 'set_colour requires an argument'
        unless @_;

    $this->{colour} = shift;
}

# if you like combined setter/getters
use Scalar::Util qw(reftype);

sub colour {
    my $this = shift;

    if ( @_ ) {
        my $arg = shift;
        croak 'Illegal value for method colour'
            unless reftype $arg eq 'ARRAY';
        $this->{colour} = $arg;
    }

    return @{ $this->{colour}||[] };
}
[download]

Some people prefer 'duck-typing' to checking reftype of a value. The basic idea is that if it quacks, it's a duck. So, to test if something is an array, we try treating it like one. If it works, then it's an array (even if it's really a tied hash behind the scenes).

sub colour {
    my $this = shift;

    if ( @_ ) {
        my $arg = shift;
        local $@;  
        croak 'Illegal value for method colour'
            unless eval { @$arg; 1 };
        $this->{colour} = $arg;
    }

    return @{ $this->{colour}||[] };
}
[download]