Creating a derived object from an existing base object in .net

Question

Dumb question.

Lets say I have a bunch of person objects with their fields all filled in with data and I have an employee type that derives from the person class and has extra fields related to being an employee. How do I get a employee object for a particular existing person object? i.e. How do I pass in the person object to the employee?

Answer 1

If the person was created as an employee, then just cast:

Person person = new Employee(); // for some reason
...
Employee emp = (Employee)person;

If the person is just a person: you can't; you could have the employee encapsulate the Person - or you can copy the fields:

class Employee { // encapsulation
  private readonly Person person;
  public Person {get {return person;}}
  public Employee(Person person) {this.person = person;}
  public Employee() : this(new Person()) {}
}

or

class Employee : Person { // inheritance
  public Employee(Person person) : base(person) {}
  public Employee() {}
}
class Person {
    public Person(Person template) {
        this.Name = template.Name; // etc
    }
    public Person() {}
}