using System;

​

interface ICovar<out T> {

    T Get();

    // void Set(T value); // Can't have arguments of covariant type

}

​

interface IContravar<in T> {

    // T Get(); // Can't have return type of contravariant type

    void Set(T value);

}

public class Program

{

    public static void Main()

    {

        {

        //===============================================================

        // Covariance

        //===============================================================

            // ICovar<T> means ICovar<any-type-that-inherits-from-T>

            ICovar<string> str = null;

            ICovar<object> obj = null;

​

            // str = obj; // Bad: object does NOT inherit from string(T)

            obj = str; // Good: string DOES inherit from object(T)

        }

        {

        //===============================================================

        // Contravariance

        //===============================================================

            // IContravar<T> means IContravar<any-type-T-inherits-from>

            IContravar<string> str = null;

            IContravar<object> obj = null;

​

            str = obj; // Good: object IS a base class of string

            // obj = str; // Bad: string is NOT a base class of object

        }

    }

}