#derived

Flags whose designs were derived from the Cross of Burgundy

“It is also used to describe the distinctive vanilla flavor derived from V. planifolia grown successfully in tropical countries such as India.”

Holly Doyle in Bernhard Knauer’s Derived, Sydney Dance Company, December 2015. © Peter Greig.

Template, or Generic, classes in C# are a handy way of providing type safety, Template classes also help code look clean and readable (As anyone who has coded in KNR C or C++ with complex types.

There will be occasions when you want to extend a template class.  

I recently wanted to extend one of the basic template classes in C#

public class FunList : LinkedList<MyType>

{

    // ToString is a static function, overriding can be done simply

    // by using the override keyword

    public override string ToString()

    {

        // Do stringy things 

    }

    // Clear is not a static function, 

    // meaning that it fiddles with internal variables, that means state  

    public new void Clear()

    {

        // Handy way to call parent class in over-ride, works for templates too                ((LinkedList<MyType>)this).Clear();

    }

}

So, the trick is knowing if the function you are calling diddles class state variables. For classes you don’t write, you get to rely on the compiler to tell you how you override. 

There are two keywords you can use to override a base class, “new” and “Override”

“Override” should not be used for functions that modify the state of the class, most of the libraries functions are declared such that you can’t override functions that mess about with internal variables. 

New use for New

This was a new one on me (pun trifecta), using the keyword new in the declaration of a  function overrides and supersedes a parent class’s function with the same name. In this example overriding the base LinkList<T> class’s Clear() function. 

Come to your own rescue: Typecast yourself. 

One of the benefits of templates is that you don’t have to typecast parameters and return values, but how the hell do you get a handle on the instance of your parent class when you are overriding... When you type cast “this” to the type of your Base Class vola, you have a pointer to the instance of your base class.