I hope to get a specific instance when I use my static method. For example:
class Food: NSObject {
var name: String
class func initFruit() -> Food? {
let fruitName = NSStringFromClass(self).components(separatedBy: ".").last! as String
if "Apple" == fruitName {
return Apple(name: fruitName)
} else if "Orange" == fruitName {
return Orange(name: fruitName)
}
return nil
}
init(name: String) {
self.name = name
}
}
class Apple: Food {
}
class Orange: Food {
}
When I create an Apple instance with the method:
let apple = Apple.initFruit() as? Apple
How can I get the specific instance apple rather than use as? Apple?. I wonder how to modify the method:
static func initFruit() -> Food?
There are a couple of problems with your design, let me try and enumerate them:
Leaving all those aside, you can use Self as return type for the static method, this will allow dynamic results.
class Food: NSObject {
var name: String
class func initFruit() -> Self {
let fruitName = NSStringFromClass(self).components(separatedBy: ".").last! as String
return self.init(name: fruitName)
}
required init(name: String) {
self.name = name
}
}
class Apple: Food {
}
class Orange: Food {
}
let apple = Apple.initFruit() // is an Apple, no cast needed
i think it's not good idea because Food is parent class and Apple inherits Food. Apple may know it's parent class cause is extends Food but Food does not.
So, if you want to create instance by some string or some variable. I would like to recommend you to adopt "Factory pattern"
reference here: https://medium.com/swift-programming/design-patterns-creational-patterns-factory-pattern-in-swift-d049af54235b
Inspired by the question Generics in Swift - "Generic parameter 'T' could not be inferred I find another way to resolve this question. I add a method to infer the specific type.
func ascertainFruitType<T>() -> T {
return self as! T // as! is dangerous
}
Then the method initFruit is changed on below:
class func initFruit() -> Self {
let fruitName = NSStringFromClass(self).components(separatedBy: ".").last! as String
if "Apple" == fruitName {
return Apple(name: fruitName).ascertainFruitType()
} else {
return Orange(name: fruitName).ascertainFruitType()
}
}