for completeness:

you can even slice lists ...

sub defaults {
  my ($d1,$d2,$d3) = ( @_ , (1,2,3)[@_ .. 2] );
  print("$d1 $d2 $d3\n");
}
  
defaults();
defaults(0);
defaults(0, 0);
defaults(0, 0, 0);
[download]

but I don't like that the maximum index has to be hard coded.

at least this solution doesn't destroy @_ ...