Methods with ref this-intent are not inherited

[e-kayrakli]

class Parent {
  var x = 1;
  proc ref increment() { x += 1; }
}

class Child: Parent { }

var c = new Child();
c.increment();
writeln(c);

doesn't resolve with:

$CHPL_HOME/refIntentInherit.chpl:1: In module 'refIntentInherit':
$CHPL_HOME/refIntentInherit.chpl:9: error: unresolved call 'unmanaged Child.increment()'
$CHPL_HOME/refIntentInherit.chpl:3: note: this candidate did not match: ref Parent.increment() [319122]
$CHPL_HOME/refIntentInherit.chpl:9: note: because method call receiver with type 'unmanaged Child'
$CHPL_HOME/refIntentInherit.chpl:3: note: is passed to formal 'ref this: borrowed Parent [319124]'
$CHPL_HOME/refIntentInherit.chpl:9: note: unresolved call had id 319166

You don't literally have to modify the field to reproduce. A method that just writeln doesn't work either, as long as it has ref this intent.

[DanilaFe]

My initial guess is that this could be a correctness issue, for the same reason we disallow subtyping with ref arguments in general. Specifically, it's the object slicing problem.

[bradcray]

I think Daniel's probably right, but for me this case raises a question as to whether—to support inheritance-like behavior and productivity—we should have the compiler stamp out

proc ref Child.increment() { super.x += 1; }

The only sticky issue I can think of is whether this causes problems if Child has a tertiary method named increment() (which we couldn't necessarily know when compiling the module it was defined in).