Here's the question you have to ask yourself - how often do you expect to be changing the values of an attribute? Personally, when I create a circle, I don't expect to be changing its radius. I definitely don't expect to set its area. I already created the damn thing - why should I have to tell it how big it is?? It has eyes and a brain - it should tell me! Maybe something like this would be more to your liking:

package Circle;

my $PI = 3.1415926;

sub new {
    my $class = shift;
    my ($radius) = @_;

    return bless {
        radius => $radius
    }, $class;
}

sub radius {
    my $self = shift;
    return $self->{radius};
}

sub area {
    my $self = shift;
    return $PI * $self->radius ** 2;
}

sub stretch {
    my $self = shift;
    my ($amount) = @_;

    $self->{radius} += $amount;

    return;
}
[download]

You'll note the stretch() subroutine - that allows you to alter the size of the circle. But, instead of re-setting the radius, you're $cicle->strech( 3 )'ing, which makes more sense from a reader's point of view.

Most accessors in Perl are there for the object itself, not for the client. In Ruby, for instance, I would write that Circle class as so:

class Circle
    attr_reader :radius

    @@PI = 3.1415926
    @@PI.freeze

    def initialize ( r = 5 )
        @radius = r
    end

    def area
        @@PI * @radius * @radius
    end

    def stretch ( amount = 1 )
        @radius += amount
    end
end
[download]

@x is an instance attribute and @@X is a class attribute. freeze() marks it as a constant. The ( x = 1 ) in the method declarations are default values.

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