What is the DRY principle?

Redundancies in process and logic

DRY addresses two common forms of repetition:

• Redundant processes. This refers to repeated actions or workflows that can be streamlined or automated. By consolidating steps and introducing automation, teams reduce inefficiencies and errors.
• Redundant logic. This occurs when similar or identical code is written in multiple places. Abstraction -- through functions, classes or modules -- helps centralize functionality, allowing changes to propagate system-wide with minimal effort.

This focus on maintainability ensures that developers can make updates in one location and have them consistently applied throughout the system.

Why DRY matters

Following the DRY principle brings several tangible benefits.

First, it improves maintainability and consistency, making it easier for developers to update codebases without introducing bugs. It also leads to greater readability and collaboration across development teams. Finally, it reduces the risk of copy-and-paste errors, which can occur when duplicated code is not consistently updated.

However, developers must balance DRY with practicality. Over-abstraction, particularly when done prematurely, can lead to convoluted code that's difficult to understand and maintain. This is why many developers follow the rule of three -- wait until code is repeated at least three times before abstracting it.

DRY versus WET, AHA and other principles

The DRY principle is often contrasted with several other principles:

• WET (write everything twice or we enjoy typing). This is the opposite of DRY, and implies that code duplication is common, usually at the cost of maintainability.
• AHA (avoid hasty abstractions). AHA is a more flexible philosophy that discourages premature abstraction in favor of gradual, well-considered generalization.
• SRP (single responsibility principle). A part of SOLID design principles, SRP ensures each module or class has one purpose, complementing DRY by reinforcing modularity and focus.

While DRY aims to eliminate repetition, these related principles offer guidelines for how and when to abstract code in a maintainable way.

How to apply DRY effectively

To put DRY into practice, developers should adhere to the following:

• Use functions, methods or modules to encapsulate repeated logic.
• Apply the rule of three to avoid premature abstraction.
• Refactor similar code into templates, shared utilities or classes.
• Avoid repeating configuration, documentation or business rules across systems.
• Normalize databases to prevent data duplication.
• Use automation tools to reduce repeated manual steps in development workflows.

These techniques help developers create systems that are more scalable, testable and adaptable to change.

Discover how coding standards boost quality and efficiency in software projects by following conventions that support the five pillars of code quality.