Question

Code:

abstract class Parent{
    void changeChild(){

    }
}
class Child1: Parent{
}
class Child2: Parent{
}
//-----
Parent parent = new Child1(); //instantiated as Child1
parent.changeChild(); //change type of this class to Child2

so parent should be instance of Child2 class.

I understand that Child1 can be different from Child2(more/less fields, methods),
but I just want to call constructor on this object, which is not allowed.

simple

parent = new Child2();

could be done, but there is like 10 child classes(Growing) and I want to move this into parent class

Is this somehow possible in c#?

Thanks

Answer 1

You can’t change the type of an existing object, but you can create a new object and return it.

Example:

abstract class Parent{

  Parent ChangeChild<T>() where T : Parent {
    if (typeof(T) == typeof(Child1)) {
      return new Child1(this);
    if (typeof(T) == typeof(Child2)) {
      return new Child2(this);
    } else {
      throw new NotImplementedException("Unhandled type");
    }
  }

}

class Child1: Parent{
  public Child1() {} // create
  public Child1(Parent source) {} // convert
}

class Child2: Parent{
  public Child2() {} // create
  public Child2(Parent source) {} // convert
}

Parent parent = new Child1();
parent = parent.ChangeChild<Child2>();