Ingo Blechschmidt wrote:
Hi,

so we had junctions of Code references some days ago, what's with
junctions of Class and Role objects? :)

I like them! In the type lattice A|B is the lub (lowest upper bound) of A and B. And A&B is the glb (greatest lower bound) of A and B. Both are cases of multiple inheritance with possible conflicts. But A|B is more general than each of A and B, while A&B is more specific than both.


  role A { method foo() { 42 } }
  role B { method foo() { 23 } }
  class Test does A|B {}

Here you have to implement &Test::foo. Not doing so is a compile time error---or more precisly a class composition time error.


  my Test $test .= new;
  my $ret = $test.foo; # 42|23?

Whatever &Test::foo returns.


  role A {}
  role B { method foo() { 42 } }
  class Test does A|B {}

Here is no conflict, but it might be necessary to implement the more general behaviour.


  my Test $test .= new;
  my $ret = $test.foo; # unthrown-exception undef|42?

No, $ret == 42 unless Test::foo() is implemented and returns something else.


Regards, -- TSa (Thomas Sandla▀)




Reply via email to