I was helping a coworker the other day with some object oriented design issues in PHP and thought it would be great to share with the general PHP community as the general PHP community seems to lack in good OOP skills.

The task, which will be detailed later when we release it, boiled down to having a collection of files we needed to perform an operation on. Sometimes the entire collection, sometimes just a subgroup. Currently the system will only support 1 kind of file however in the very near future a new file will be added. My coworker tackled it well but a few problems that I helped him out with. Namely he made a few common mistakes in the design that most PHP developers make, namely being inconsistent with naming/etc. and not utilizing Interfaces and argument type-hinting to enforce good design, as well as putting logic in the wrong classes.

One of the few pitfalls that did happened was placing the render() function in the collection class. While this would not be a problem for a single type, when extending the system to handle n node types we come across unnecessary complexity issues in adding to the render() function, as well as making it nigh-impossible to keep the original includes intact (so as to make upgrades work without the hassle of merging code).