After sleeping on this I agree. Using some would hurt searchability and describes the feature no better than opaque does. If we go with opaquetype then IMO the type should have to be given a name explicitly, so -> opaquetype Collection where _.Element == Int would be disallowed.
There have been proposed syntaxes that would allow this sort of behavior, either via a typealias or some other annotation of the return type, so that something like this would be legal:
typealias opaque Q: A where B: C = MyConcreteType
func d() -> Q {
return ...
}
func e() -> Q {
return d()
}
func f() -> e().ResultType {
e()
}
let f = [d(), e(), f()] // OK!
Does this address your concerns?
For the same reason I've soured somewhat on some, I think this would be even worse. Single quotes don't suggest any meaning at all, and don't even really mirror any other syntax related to this feature. With Array and Dictionary shorthand, you can at least argue that the terse syntax mirrors the construction of a literal, and with Optional the shorthand mirrors Optional chaining. Furthermore, with the forward motion on character integer literals, we would be introducing two entirely unrelated uses of single quotes.