To explain this pattern, I’m going to jump into an example first and then discuss the pattern itself. Hope you don’t mind!
Suppose you have parsed a mathematical expression (with the use of the Interpreter pattern, of course!) composed of double values and addition operators, for example:
(1.0 + (2.0 + 3.0))
This expression can be represented using an object hierarchy similar to the following:
public abstract class Expression { /* nothing here (yet) */ }
public class DoubleExpression : Expression
{
private double value;
public DoubleExpression(double value) { this.value ...
