How to restrict passed parameter in method

Question

My question is in sample code. How to i restrict developers for passing true parameter. I try something about generics but i couldn't fix.

The important thing here is i want to restrict in Compile Time. So i know how can i prevent in Runtime.

namespace TheLiving
{
    public interface IFood
    {
        int Protein { get; set; }
        int Carbohydrate { get; set; }
    }

    public interface IMeat : IFood
    {
        int Nitrogen { get; set; }
    }

    public interface IVegetable : IFood
    {
        int Vitamin { get; set; }
    }


    public class Veal : IMeat
    {
        public int Protein { get; set; }
        public int Carbohydrate { get; set; }
        public int Nitrogen { get; set; }
    }

    public class Spinach : IVegetable
    {
        public int Protein { get; set; }
        public int Carbohydrate { get; set; }
        public int Vitamin { get; set; }
    }

    public interface IEating
    {
        void Eat(IFood food);
    }

    public class Lion : IEating
    {
        public int Protein { get; set; }
        public int Carbohydrate { get; set; }
        public int Nitrogen { get; set; }


        //But lion is eating only Meat. So any developer can pass vegatable to lion for eating. 
        //May be god is not a good developer. So i want restrict him on Compile Time!! for passing only Meat. :)
        //The important thing here is i want restrict on Compile Time not RunTime!!!
        public void Eat(IFood food)
        {
            Protein = food.Protein;
            Carbohydrate = food.Carbohydrate;
            //Nitrogen = ?? //So i know that i can cast and validate food but i want ensure this on DesignTime!!
        }
    }

    public class Sheep : IEating
    {
        public int Protein { get; set; }
        public int Carbohydrate { get; set; }
        public int Vitamin { get; set; }

        public void Eat(IFood food)
        {
            Protein = food.Protein;
            Carbohydrate = food.Carbohydrate;
            //Vitamin = food.??
        }
    }
}

Answer 1

I think you'll have to have interfaces for IHerbivore , ICarnivore , and IOmnivore to allow this at design time.

public interface IHerbivore
{
    void Eat(IVegetable food);
}

public interface ICarnivore
{
    void Eat(IMeat food);
}

public interface IOmnivore : IHerbivore, ICarnivore
{
}

Then your lion can be an ICarnivore and will only be able to eat meat

Answer 2

Alternative you can change the interface...

public interface IEating
{
    bool Eat(IFood food); //return wheater the eater eats the food or not
}

And implement the lion like:

public class Lion : IEating
{
    public int Protein { get; set; }
    public int Carbohydrate { get; set; }
    public int Nitrogen { get; set; }

    public bool Eat(IFood food)
    {
        IMeat meat = food as IMeat;
        if (meat != null)
        {

            Protein = meat.Protein;
            Carbohydrate = meat.Carbohydrate;
            Nitrogen = meat.Nitrogen;
            return true;
        }
        return false;
    }
}

Answer 3

public interface IEating<in T> where T : IFood {

    void Eat(T food);
}

public class Lion : IEating<IMeat>, IEating<IFood> {

    public int Protein { get; set; }
    public int Carbohydrate { get; set; }
    public int Nitrogen { get; set; }

    public void Eat(IMeat food) {

        Protein = food.Protein;
        Carbohydrate = food.Carbohydrate;
        Nitrogen = food.Nitrogen;
    }

    public void Eat(IFood food) {

        var meat = food as IMeat;
        if (meat == null) return;

        Eat(meat);
    }
}

public class Sheep : IEating<IVegetable>, IEating<IFood> {

    public int Protein { get; set; }
    public int Carbohydrate { get; set; }
    public int Vitamin { get; set; }

    public void Eat(IVegetable food) {
        Protein = food.Protein;
        Carbohydrate = food.Carbohydrate;
        Vitamin = food.Vitamin;
    }

    public void Eat(IFood food) {

        var vegetable = food as IVegetable;
        if (vegetable == null) return;

        Eat(vegetable);
    }
}

Answer 4

What about MS Code Contracts ? I would swear its Visual Studio integration add at least warnings at compile time.