Swift/iOS: How to access Object properties when type-casted from Protocol?

for type in types {
    if let fooType = type as? Foo.Type {
        // in Swift 2 you have to explicitly call the initializer of metatypes
        let obj = fooType.init(foo: "special snowflake string")
    }
}

for case let type as Foo.Type in types {
    let obj = type.init(foo: "special snowflake string")
}

class Foo {}

protocol JSONInitializable {
    static func initialize(fromJSON: [String : AnyObject]) throws -> Self?
}

extension Foo: JSONInitializable {
    static func initialize(fromJSON: [String : AnyObject]) throws -> Self? {
        return nil
    }
}

struct Foo: JSONInitializable {
    static func initialize(fromJSON: [String : AnyObject]) throws -> Foo? {
        return nil
    }
}

enum Foo: JSONInitializable {
    case One, Two, Three

    static func initialize(fromJSON: [String : AnyObject]) throws -> Foo? {
        return nil
    }
}

protocol ProtocolA {
    associatedtype BType: ProtocolB
    var b: BType? { get } // Note the change in the type of b
}

extension A: ProtocolA {
    typealias BType = B
}

var protocolA: ProtocolA? // error