Question

In C# I have three classes: Person, Cat, and Dog.

Both the Cat and Dog classes have the method Eat().

I want the Person class to have a property ‘Pet’.

I want to be able to call the Eat method of both the Cat and Dog via the Person via something like Person.Pet.Eat() but I can’t because the Pet property needs to be either of type Cat or Dog.

Currently I’m getting round this with two properties in the Person class: PetDog and PetCat.

This is okay for now, but if I wanted a 100 different types of animal as pets then I don’t really want to have 100 different Pet properties in the Person class.

Is there a way round this using Interfaces or Inheritance? Is there a way I can set Pet to be of type Object but still access the properties of whichever animal class is assigned to it?

Answer 1

You could have the pets derive from a common base class:

public abstract class Animal
{
    protected Animal() { }

    public abstract void Eat();
}

And then have Cat and Dog derive from this base class:

public class Cat: Animal
{
    public override void Eat()
    {
        // TODO: Provide an implementation for an eating cat
    }
}

public class Dog: Animal
{
    public override void Eat()
    {
        // TODO: Provide an implementation for an eating dog
    }
}

And your Person class will have a property of type Animal:

public class Person
{
    public Animal Pet { get; set; }
}

And when you have an instance of Person:

var person = new Person 
{
    Pet = new Cat()
};
// This will call the Eat method from the Cat class as the pet is a cat
person.Pet.Eat();

---

You could also provide some common implementation for the Eat method in the base class to avoid having to override it in the derived classes:

public abstract class Animal
{
    protected Animal() { }

    public virtual void Eat()
    {
        // TODO : Provide some common implementation for an eating animal
    }
}

Notice that Animal is still an abstract class to prevent it from being instantiated directly.

public class Cat: Animal
{
}

public class Dog: Animal
{
    public override void Eat()
    {
        // TODO: Some specific behavior for an eating dog like
        // doing a mess all around his bowl :-)

        base.Eat();
    }
}