Question

为什么跟随is检查错误？

class Person : BaseClass { ... }
class Parent : Person { ... }
.
.
let parent = Parent()
print("parent is BaseClass: \(parent.self is BaseClass)")
// this prints 'parent is BaseClass: false'

如何检查子类的基类或超类？特别是如果我不知道对象的子类有多深。

更新：我的错误以下是真的

print("parent is BaseClass: \(parent.self is BaseClass)")
// this prints 'parent is BaseClass: true'

但这个不是

class GenericClass<T: BaseClass> { }
.
let myGeneric = GenericClass<Parent>()
print("myGeneric is GenericClass<BaseClass>: \(myGeneric.self is GenericClass<BaseClass>)")
// this prints 'myGeneric is GenericClass<BaseClass>: false'

在Playground我收到以下警告：

Playground.playground：从'GenericClass'转换为不相关的类型'GenericClass'总是失败

那么如何检查基类的泛型关系呢？

Answer 1

您必须将包含的类型公开为typealias。这是解决方案。

protocol BaseClass { }
class Person : BaseClass { }
class Parent : Person { }

class GenericClass<T: BaseClass> {
    typealias Contained = T
}

let myGeneric = GenericClass<Parent>()
print("myGeneric is GenericClass<BaseClass>: \(type(of: myGeneric).Contained() is BaseClass)")

Swift：如何在子类上检查基类和超类

1 个答案: