Professional PHP Design Patterns

7.1. Problem and Solution

Most PHP programmers have started out working with a very procedural type of programming. This style of programming relies heavily on flow control based on conditional statements. Object Oriented Programming provides some avenues to move beyond traditional conditional statements to create a more polymorphic code stream. One of the ways to implement this is by creating objects based on the Delegate Design Pattern.

The Delegate Design Pattern focuses on removing complexity from core objects. Instead of designing an object to rely heavily on executing specific functionality by evaluating a conditional statement, the object can delegate the decision to different objects. This can be as simple as having an intermediate object to process the decision tree to as complex as having objects instantiated dynamically to provide the desired functionality.

It is important not to view the Delegate Design Pattern as a direct competitor to the conditional statement. Instead, the Delegate Design Pattern helps form the architecture in such a way that conditional statements aren't needed to invoke the proper functionality. They're encouraged to reside in the actual methods, where they can be tasked to process business rules.

An example of when the Delegate Design Pattern should be used is when providing multiple formats for a specific piece of data. Imagine an archive at an open source code repository. When the visitor intends to download a portion of that code, they have ...