Swift: types for composition type

In Objective-C, I can declare a class as a subclass and conform to the protocol:

@interface SubClass : ParentClass<OneProtocol>

      

        
        
        
      

    

When migrating to Swift 1.x, SubClass

it becomes

class SubClass : ParentClass, OneProtocol

      

        
        
        
      

    

I find it difficult to use this type of composite type. For example, without using generics, how do you say the function returns an instance ParentClass

that matches OneProtocol

?

I know if these are two protocols we can use protocol<OneProtocol, TwoProtocol>

. But here one of them is a class.

Ideally there is a syntax for declaring this as typealias. But if this is not possible, in the latter case you need to compose Objective-C and combine composition with Swift.