Subscribe to PHP Freaks RSS The DRY principle misunderstood

syndicated from on February 23, 2018

On the site there's a new tutorial posted that talks about the DRY principle in development (Don't Repeat Yourself) and why you might be misunderstanding the intent.

I know what you are thinking: "Again a boring article on DRY? Don't we have enough already?". You might be right. However I see too many developers (junior or senior) applying DRY like they are doing some witch hunting. Totally randomly or everywhere they can. So apparently we never have enough DRY principle articles on Internet.

A little reminder for those in the back who don't follow: the DRY principle means "Don't Repeat Yourself" and was first introduced in the The Pragmatic Programmer. The principle itself was known and applied before this book came to life. However the Pragmatic Programmer defined it precisely and put a name on it.

He starts by defining the original intent of the principle: not repeating knowledge (not necessarily repeating code). He gives an example of a e-commerce site and the logic around "shipments". If there's logic around these shipments happening in multiple places in the application, that can lead to maintenance issues down the line. He suggests creating a single instance of the knowledge about shipment handling rather than just reducing code duplication. He gives an example of a product instance and code duplication happening in some of the data validation. After showing a possible solution for this particular issue he gets into some issues that come from over-DRYing your code including useless abstractions and premature optimization.