Patterns are useful

This is not a book about the theory behind patterns; rather, this book focuses on the aspects of their implementation. Before I scare you all off with all this talk about design patterns, their history, modern advances, anti-patterns, and so on, I have decided to present a very simple pattern using an example. A few lines of code should explain why a pattern—based approach to problem solving can be a good thing.

In the code archive for this chapter, you'll find a simple console application called DesignPatternExample. Inside, you'll find an implementation of a sparse array, as shown in the following code fragment:

type
  TSparseRec = record
  IsEmpty: boolean;
  Value : integer;
end;

TSparseArray = TArray<TSparseRec>;

Each array index can either be empty (in which case IsEmpty will be set to True), or it can contain a value (in which case...