Swift 中如何判断实例变量的类是什么

：

swift
class Animal {
    func makeSound() {
        print("Animal is making a sound.")
    }
}
class Cat: Animal {
    override func makeSound() {
        print("Cat is meowing.")
    }
}
class Dog: Animal {
    override func makeSound() {
        print("Dog is barking.")
    }
}
let animal: Animal = Cat()
if animal is Cat {
    print("The animal is a cat.")
} else {
    print("The animal is not a cat.")
}

swift
let animal: Animal = Cat()
if let cat = animal as? Cat {
    cat.makeSound()
} else {
    print("The animal is not a cat.")
}