如何在Swift2中使用泛型类型

Question

I'm not familiar with the generic type in swift and then I try to study and practice but I encountered an error in compiler. take a look addNewType() method in ObjectA class. Does anyone can help me? thanks!

class TypeA: NSObject {

    override init() {
        print("typeA")
    }
}

class ObjectA<T: TypeA>: NSObject {

    var type = [T]()

    init(type:T) {
        self.type.append(type)
    }

    func addNewType() {
        let newType = TypeA()
        self.type.append(newType) <-- Cannot invoke "append" with an argument list of type '(TypeA)'
    }
}

Answer 1

type is an array of type T . That means all elements must be of type T . In the addNewType() method, you try appending an element of type TypeA to the array of type T . That is a type mismatch. You can only put T s in the array, but you are trying to add a TypeA . This causes the error.

If you want to let TypeA s be put in the array as well then define it as var type = [TypeA]() . Because T is defined to be a subclass of TypeA , you can then put instances of both T and TypeA in the array.