[Patterns] Ambiguity with the wildcards in object patterns

[sgrekhov]

Patterns spec says nothing about the case when class contains a getter named _ (or, at least, I didn't find it in the spec). What should we expect in the following case?

class C {
  int get _ => 42;
}

main() {
  C c = C();
  switch (c) {
    case C(:var _): print(_);
  }
}

Did we declare here a variable named _ and the programm will print 42? Or _ is always a wildcard and print(_) is a compile time error?

[lrhn]

The _ is always a wild card in a pattern. You'll have to write case C(_: var underscore): ... to read that particular getter. The _ in the name part is a plain identifier, not a pattern.

We should probably say that C(:var _) is invalid, because it does not introduce an implicit name for a getter to read.

[leafpetersen]

We should probably say that C(:var _) is invalid, because it does not introduce an implicit name for a getter to read.

I at least attempted to specify this here (see the added section on name inference and the two references to it).

[lrhn]

My bad, I should have checked that we didn't already do it, before saying that we "probably should". We should, and we do, and that's good!

[sgrekhov]

Ah, it is specified that it is a compile-time error. Sorry, didn't notice that. I'll add appropriate tests. Closing this issue

[leafpetersen]

Ah, it is specified that it is a compile-time error. Sorry, didn't notice that. I'll add appropriate tests. Closing this issue

I'm trying to remind myself to cc you when we make spec changes, but I usually forget. Sorry. :(