如何在协议A的扩展中检查“self”是否遵循协议B？

Question

设计模式看起来像这样：

protocol Base {

}

protocol A: Base {

}

protocol B: Base {

}

extension A {
    func someFunc() {
        if ((self as Any) is any B.Type) { // <- apparently this compiles, but doesn't return True as it's designed in extension A, not the real class that both follows A and B
            print("So it also follows protocol B")
        }
    }
}

class finalClass: A, B {
    func anotherFunc() {
        someFunc()
    }
}

我想检查扩展 A 的定义，调用该函数的类是否也遵循协议 B？

我意识到使用

as?

可以工作，但是这里有一定的模式或最佳实践吗？

Answer 1

您需要定义“实际上不起作用”。其他人看到它有效但不理解。

extension A {
  func someFunc() -> String { "A" }
}

extension A where Self: B {
  func someFunc() -> String { "B" }
}

final class AClass: A { }
final class ABClass: A & B { }

AClass().someFunc() // "A"
ABClass().someFunc() // "B"