如何在泛型类中使用类类型

Question

From a log file I obtain a string that contains the name a class, eg "Child" that may be defined as:

class Child: Object, MyProtocol {
// ...
}

I want to use this class in the following generic class:

open class MyClass<T: Object> where T:MyProtocol {
    //…

    open class func doSomething() {
    //…
    }

}

I already asked a question here how to obtain the class type from a string, which can be obtained by:

let objectType = NSClassFromString("MyModule.\(strFromLog)”) as! Object.Type

Obviously, objectType can not be used directly on MyClass since it is of type T.Type and not T , and the following does not work:

MyClass<objectType>.doSomething() // -> error: Use of undeclared type 'objectType'

However, is there still a way to use objectType in MyClass without the need to change the generic class itself (ie other methods rely on it)?

Answer 1

Unfortunately you can't use result of NSClassFromString as a type for your generic class. However, you can workaround this by writing something like this:

protocol SomeProtocol {
}

extension NSString: SomeProtocol {
}

class SomeClass<T: SomeProtocol> {
  class func doSomething() {
  }
}

if let some = NSClassFromString("NSString") {
  if some is NSString.Type {
    SomeClass<NSString>.doSomething()
    print("String")
  } else {
    print("Not String")
  }
}