Mastering Delphi Programming: A Complete Reference Guide

Don't repeat yourself

The don't repeat yourself principle (DRY), states that every piece of knowledge should have a single representation within a system. In other words, you should implement each small part of functionality as one method, and not use copy and paste.

In practice, such detailed decomposition will also cause problems. We will usually use a function from multiple places in the code. If that shared function changes behavior, we have to explicitly check all call sites (all places that use it) to see whether the new functionality is indeed required and desired at that place. Still, this is much better than the mess introduced by copy and paste programming.