MetaTypes.md

Swift Meta types

• type(of:) Returns the Type of the object (dynamic type)

• .Type Dog.Type means that the Dog type itself is expected (or the type of one of its subclasses), not a instance!

• .self To pass the Dog type where Dog.Type is expected, you can pass Dog.self.

• self the current instance

• Self An instance of whatever type this is at runtime

class Animal {
    var name : String

    init() {
        name = "Giraff"
    }

    //Every subclass of Animal must inherit or reimplement init(name:)
    required init(name:String) {
        self.name = name
    }

    // class method & factory method
    // Self - "an instance of whatever type this is at runtime."
    // self - in a class methods, refers to the static type
    class func makeAndName() -> Self {
        return self.init(name:"Fido")
    }

    // in normal methods, not class methods, use type(of:) on the instance to get type and then init
    func havePuppy(name:String) -> Self {
        return type(of:self).init(name:name)
    }

}

class Dog : Animal {
    var race : String

    override init() {
        race = "bulldog"
        super.init()
    }

    required init(name: String) {
        race = "pincher"
        super.init(name: name)
    }
}

func createAnimalInstance(of typeName: Animal.Type) -> Animal {
    //the compiler is in doubt as to whether the init(name:) initializer is implemented by every possible subtype of Animal. To reassure it, we must declare that initializer with the required keyword

    return typeName.init(name: "unanmed")
}

let dog = createAnimalInstance(of: Dog.self)
//dog.race  //will not compile since dogs static type is Animal but dynamic type is Dog

let name = type(of:dog)  //Returns the dynamic type which in this case is Dog

let anotherDog = Dog()
let puppy = anotherDog.havePuppy(name: "tommy")


let animal1 = Animal.makeAndName()
let animal2 = Dog.makeAndName()
animal2.race

type(of:animal2)