Why can't reference to child Class object refer to the parent Class object?

Question

I was explaining OOP to my friend. I was unable to answer this question. (How shameful of me? :( )

I just escaped by saying, since OOP depicts the real world. In rea

Answer 1

The assignments you are performing are called downcasting and upcasting. Downcasting is what happens when you cast an object to a String. Upcasting is the opposite where you are casting a type to a more general type. Upcasting never fails. Downcasting is only valid up until the point where you are downcasting to a type more specific than what the object was instantiated as.

class Named
{
    public string FullName
}

class Person: Named
{
    public bool IsAlive
}

class Parent: Person
{   
   public Collection Children
}

class Child : Person 
{  
   public Parent parent;
}

public static void Main()
{
  Named personAsNamed = new Person(); //upcast
  Person person = personAsNamed ; //downcast
  Child person = personAsNamed ; //failed downcast because object was instantiated
  //as a Person, and child is more specialized than(is a derived type of) Person
  //The Person has no implementation or data required to support the additional Child
  //operations. 
}