Understanding the Factory Method pattern

The Factory pattern, or Factory Method pattern, is a creational design pattern that allows the creation of objects without needing to specify the exact (derived) class that will be instantiated. A Factory Method pattern provides an interface for creating an object, yet allows details within the creation method to decide which (derived) class to instantiate.

A Factory Method pattern is also known as a virtual constructor. Much as a virtual destructor has the specific destructor (which is the entry point of the destruction sequence) determined at runtime through dynamic binding, the concept of a virtual constructor is such that the desired object to instantiate is uniformly determined at runtime.

We cannot always anticipate the specific mix of related derived class objects needed in an application. A Factory Method (or virtual constructor) can create, upon request, an instance of one of many related derived class types, based on the input...