Question

I am trying to design an object model (for C#), and can’t work out the best way to store the data. I’ll try to use a simple example to illustrate this!

I have an object ‘pet’, which could be one of, ‘cat’, ‘dog’ etc. So I have created an ‘pet’ class with a ‘petType’ enum to store this.

Now this is where it gets tricky. If an ‘pet’ is a ‘cat’, then its ‘food’ could be one of ‘fish’, ‘milk’ etc. If it is a ‘dog’ then its ‘food’ could be ‘meat’, ‘biscuits’ or something.

Now should I create a big enum for ‘fish’, ‘milk’, ‘meat’ and ‘biscuits’ and somehow code it so that a ‘cat’ cannot be assigned ‘food.meat’? It wouldnt really make sense for my ‘pet’ class to have a ‘catfood’ and ‘dogfood’ enum, because thats not extensible and it will end up storing loads of enums that are null.

Is there an elegant solution to this that I’m not seeing?

Answer 1

Try #2. Seems to be correct

interface IPet { }  class Cat : IPet {     public void eat(CommonFood food) { }     public void eat(CatFood food) { } }  class Dog : IPet {     public void eat(CommonFood food) { }     public void eat(DogFood food) { } }  interface IFood { }  abstract class CommonFood : IFood { }  abstract class CatFood : IFood { }  abstract class DogFood : IFood { }  class Milk : CommonFood { }  class Fish : CatFood { }  class Meat : DogFood { }  class Program {     static void Main(string[] args)     {         Dog myDog = new Dog();         myDog.eat(new Milk()); // ok, milk is common         myDog.eat(new Fish()); // error     } }