ehm ... $self defaults to 1??? ;-)

IMHO better catch $self in a separate shift!

UPDATE:

> The overwhelming majority of the cases there is one parameter that is optional. Which means that the predominant use will look like this:

Then better avoid this construct!

IMHO it's much clearer (and faster) to write

my ($self,$a,$b,$c,$d)=@_;
$d = 4 unless defined $d;
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