Can’t use optional types in enumerated bounds of generic type constraints

[lucaswerkmeister]

The spec says (3.2.8, 1.0, current) that

X? means Null|X for any type X

however, you can’t actually use it in generic type constraints:

void error<Param>() given Param of Object? { } // enumerated bound must be a class or interface type
void works<Param>() given Param of Null|Object { }

I can’t find any mention of this in the section on generic type constraints (3.5.3, 1.0, current).

Is this intentional, or an oversight in the grammar/typechecker?

[gavinking]

Well if you check the definition of CaseTypes in the spec, you'll see that the thing that follows of isn't actually an arbitrary type expression. Rather, it's a list of types, with I as punctuation.

So actually this is intentional.

[lucaswerkmeister]

Okay, but then I guess it’s a bit confusing... “X? means Null|X for any type X” reads to me as if replacing X|Null with X? and vice versa should never have any effect, but in this case it does make a difference.

Actually, looking at the grammar, I don’t understand why this isn’t accepted. caseTypes takes an abbreviatedType, which includes optional types.