协议关联类型typealias赋值编译错误

Following code:

以下代码：

protocol SomeProtocol {
    typealias SomeType = Int // used typealias-assignment

    func someFunc(someVar: SomeType)
}

class SomeClass: SomeProtocol {
    func someFunc(someVar: SomeType) {
        print(someVar)
    }
}
protocol SomeProtocol