I have such simple class where I am trying to constrain the type of the object inside my class using generic type (Dog in this case). I expect to see the compilation error here box.put(cat) because I pass the wrong type but unfortunately, I don`t see any.
class Box<T>{
content: Array<T> = [];
put(animal: T){
this.content.push(animal);
}
}
var dog = new Dog();
var cat = new Cat();
var box = new Box<Dog>();
box.put(cat);
Typescript uses structural compatibility to determine type compatibility. So given your code, if Dog and Cat have these definitions
class Dog{ name: string }
class Cat{ name: string; lives: number }
Your code will work because Cat has all the fields of Dog and is thus compatible.
If you defined the classes like this:
class Dog{ name: string; isAsGoodBoy: boolean }
class Cat{ name: string; lives: number }
Your code will no longer work, because Dog has fields Cat does not.
A useful way to think about it if you are familiar with Javascript is that structural typing is the compile time version of duck typing.
