How to reference a generic class with a constraint from a Protocol with a typealias in Swift?

Question

I'm try to define a protocol P2 so that it returns a generic class with a constraint on another protocol P1, e.g:

protocol P1 {}

class C<T : P1> {}

public protocol P2 {
    typealias T
    class func c() -> C<T>
}

But this results in the following compiler error:

error: type 'T' does not conform to protocol 'P1'
    class func c() -> C<T>

There doesn't seem to be any combination that allows this, e.g. the next obvious syntax:

protocol P1 {}

class C<T : P1> {}

public protocol P2 {
    typealias T
    class func c() -> C<T : P1>
}

Errors with:

error: expected '>' to complete generic argument list
    class func c() -> C<T : P1>
                          ^
note: to match this opening '<'
    class func c() -> C<T : P1>

Is this possible to do in Swift?

Answer 1

I have never used constraints like that, but I think you can just define it in the typealias - I've tried it in a playground and compilation succeeds:

typealias T: P1