It's interesting, this is how I write them too. But I noticed lodin's node, which contains an important but subtle difference; by doing this:

sub field {
    my $self = shift;
    $self->{field} = $_[0] if @_;
    ...
}
[download]

instead of this:

sub field {
    my ($self,$val) = @_;
    $self->{field} = $val if defined $val;
    ...
}
[download]

you don't run into issues where $self->field(undef) would silently return the old value without changing it, which isn't what you might expect. But because I've seen the second form elsewhere and it's technically better practice to assign @_ to variables I just stuck with it, but clearly the first way is better.