namespace DefaultNamespace
{
    public class BaseClass {}

    public class ChildClass : BaseClass {}

    public delegate void CoVarianceHandler(ChildClass args);
    public delegate BaseClass ContraVarianceHandler();

    public class Delegates
    {
        public event CoVarianceHandler CoVariance;
        public event ContraVarianceHandler ContraVariance;
    
        public void OnBaseClass(BaseClass args) {}
        public void OnChildClass(ChildClass args) {}

        public BaseClass OnReturnBaseClass()
        {
            return new BaseClass();
        }

        public ChildClass OnReturnChildClass()
        {
            return new ChildClass();
        }

        public void Init()
        {
            CoVariance += OnBaseClass;
            CoVariance += OnChildClass;
        
            CoVariance?.Invoke(new ChildClass());
            // CoVariance?.Invoke(new BaseClass()); // is not working, because delegate expect an instance of ChildClass
        
            ContraVariance += OnReturnBaseClass;
            ContraVariance += OnReturnChildClass;
        
            BaseClass baseClass = ContraVariance?.Invoke();
            // ChildClass childClass = ContraVariance?.Invoke(); // is not working, because delegate returns only an instance of BaseClass
        }
    }
}