Ingo Blechschmidt wrote:

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 = $; # 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 = $; # unthrown-exception undef|42?

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

Regards, -- TSa (Thomas Sandla▀)

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