C# Language Tutorial => Using generic method with an interface as a...

Example

This is an example of how to use the generic type TFood inside Eat method on the class Animal

public interface IFood
{
    void EatenBy(Animal animal);
}

public class Grass: IFood
{
    public void EatenBy(Animal animal)
    {
        Console.WriteLine("Grass was eaten by: {0}", animal.Name);
    }
}

public class Animal
{
    public string Name { get; set; }

    public void Eat<TFood>(TFood food)
        where TFood : IFood
    {
        food.EatenBy(this);
    }
}

public class Carnivore : Animal
{
    public Carnivore()
    {
        Name = "Carnivore";
    }
}

public class Herbivore : Animal, IFood
{
    public Herbivore()
    {
        Name = "Herbivore";
    }
    
    public void EatenBy(Animal animal)
    {
        Console.WriteLine("Herbivore was eaten by: {0}", animal.Name);
    }
}

You can call the Eat method like this:

var grass = new Grass();        
var sheep = new Herbivore();
var lion = new Carnivore();
    
sheep.Eat(grass);
//Output: Grass was eaten by: Herbivore

lion.Eat(sheep);
//Output: Herbivore was eaten by: Carnivore

In this case if you try to call:

sheep.Eat(lion);

It won't be possible because the object lion does not implement the interface IFood. Attempting to make the above call will generate a compiler error: "The type 'Carnivore' cannot be used as type parameter 'TFood' in the generic type or method 'Animal.Eat(TFood)'. There is no implicit reference conversion from 'Carnivore' to 'IFood'."

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C# Language Generics Using generic method with an interface as a constraint type.

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