Generics.swift

import UIKit

class Pet {
    
}

class Cat: Pet {
    
}

class Dog: Pet {
    
}


public class Node<T> {
    public var value: T
    
    public init(value: T) {
        self.value = value
    }
}

var list = [Node<Pet>]()

//Error: Cannot convert value of Type Node<Dog> to expected argument type Node<Pet>
list.append(Node<Dog>(value: Dog()))