Covariance vs. contravariance with respect to class inheritance

Question

What is the meaning of the concepts \'covariance\' and \'contravariance\'?

Given 2 classes, Animal and Elephant (which inherits from

Answer 1

public interface IGoOut
{
    T Func();
}
public interface IComeIn
{
    void Action(T obj);
}
public class GoOutClass:IGoOut
{
    public T Func()
    {
        return default(T);
    }
}

public class ComeInClass : IComeIn
{
    public void Action(T obj) {  }
}

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object obj = null;
//Covariance Example [Array +  IEnumerable +  IEnumerator  +  IInterface  +  Func]
object[] array = (string[]) obj;
IEnumerable