swift - 如何使用泛型推断类型？

Question

我已经定义了一些响应模型

class UserProfile{

    var name:String = "Anish"
    var age:Int = 20
}

class StudentProfile:UserProfile{

    var std_id:Int = 1

}

我有一个用于 Web API 请求的类

class WebCaller{

    class func callWebService<T>(responseType:T.Type,completionHandler:(T)->()){

        let model =  StudentProfile() as! responseType//wont compile here
        completionHandler(model)
    }
}

我想称之为

 WebCaller.callWebService(responseType: StudentProfile.self){ responseModel in
            //response model should automatically infer the type 
            print(responseModel.name)
            print(responseModel.age)
            print(responseModel.std_id)
        }

现在如果我想调用为

 WebCaller.callWebService(responseType: UserProfile.self){ responseModel in
            //this should automaticaly infer the type
            print(responseModel.name)
            print(responseModel.age)
        }

但是，这可以使用 AnyObject 类型来完成

class func callWebService<T>(responseType:T.Type,completionHandler:(AnyObject)->())

但我需要将其转换为我的响应类型。我想要实现的是我的 API 调用者应该向我发送类型，以便我不应该将其转换为我的 ViewModel

Answer 1

T.Type 几乎无法使用，您不需要在您的场景中使用任何类型的泛型

class A{
    let typeA = "property typeA"
}
class B{
    let typeB = "property typeB"
}
class C{}

func f0(object: AnyObject) {

        if let a = object as? A {
            print(1, a.typeA)
            return
        }

        if let b = object as? B {
            print(2, b.typeB)
            return
        }
        print("unknown type")
}

f0(object: A())
f0(object: B())

func f1(object: AnyObject) {
    switch object {
    case is A:
        let a = object as! A // will never fail!!
        print(3, a.typeA)
    case is B:
        let b = object as! B // will never fail!!
        print(4, b.typeB)
    default:
        print("unknown type")
        break
    }
}

f1(object: A())
f1(object: B())

f0(object: C())
f1(object: C())

打印

1 property typeA
2 property typeB
3 property typeA
4 property typeB
unknown type
unknown type

要查看 A 和 A.Type 之间的关系，请将我们现在的内容与下一个代码片段进行比较，这会给出相同的结果

func f3(object: AnyObject) {
    switch type(of: object) {
    case is A.Type:
        let a = object as! A // will never fail!!
        print(5, a.typeA)
    case is B.Type:
        let b = object as! B // will never fail!!
        print(6, b.typeB)
    default:
        print("unknown type")
        break
    }
}

使用第一个场景可能更实用，因为您的对象中内置了一些常见的功能。

protocol Printable {
}
extension Printable {
    func p(){
        print("I am printable", type(of: self))
    }
}
class A{
    let typeA = "property typeA"
}
class B: Printable{
    let typeB = "property typeB"
}
class C: Printable{}

func f0(object: AnyObject) {
    if let p = object as? Printable {
        p.p()
    }

    if let a = object as? A {
        print(1, a.typeA)
        return
    }

    if let b = object as? B {
        print(2, b.typeB)
        return
    }

    print("unknown type")
}

f0(object: A())
f0(object: B())
f0(object: C())

打印

1 property typeA
I am printable B
2 property typeB
I am printable C
unknown type