DRY stands for Don’t Repeat Yourself, and it’s one of the oldest rules in software. The idea is simple: any piece of logic, a calculation, a business rule, a label, should be defined in one place and reused, instead of being copied across the codebase. The term comes from Andy Hunt and Dave Thomas in their 1999 book The Pragmatic Programmer.
Think of a company VAT rate written into fifty different invoices by hand. When the rate changes, someone has to track down all fifty and edit each one, and they will miss a few. The DRY version stores that rate once and every invoice reads from it, so one edit fixes everything. The same thinking keeps software honest: less duplication means fewer places for a bug to hide. This is a cornerstone of clean code and makes later refactoring far less painful.
In day-to-day code you apply DRY by pulling a repeated block into a function, a shared constant, or a reusable component. Spot the same three lines in four files, and that is your cue to give them a single name and call it everywhere.
DRY does have limits. Two snippets that look identical today might need to change for different reasons tomorrow, and gluing them together too early can backfire. The usual advice is to wait until you’ve seen the same code three times before extracting it, since a premature abstraction is often harder to undo than a little duplication. So experienced developers treat it as a guideline, not a law.
At TopDevs we apply DRY so your business rules live in one clear spot, which means changes are quick and a single fix never has to be made in ten different files.
