Introduction

The DRY (Don't Repeat Yourself) principle is one of the most fundamental guidelines in software development, advocating for code reuse and the elimination of duplication. While it's generally excellent advice, there are situations where strictly following DRY can actually lead to worse outcomes. This article explores those scenarios where you might want to think twice before applying the DRY principle.

1. When Premature Abstraction Causes More Problems

One of the most common misapplications of DRY occurs when developers create abstractions too early in the development process. Before you've seen how the code will actually be used in multiple contexts, forcing DRY can:

• Create overly complex abstractions that are hard to understand
• Introduce unnecessary coupling between components
• Make future changes more difficult because the abstraction doesn't quite fit all use cases

Better approach: Wait until you see actual duplication (rule of three) before abstracting, rather than anticipating future duplication.

2. When Readability Suffers

Sometimes, removing duplication can make code harder to understand. If extracting shared functionality means:

• Jumping through multiple files to follow the logic
• Introducing obscure naming to cover multiple use cases
• Creating "clever" but confusing solutions

...then the DRY principle might be doing more harm than good. Readable code is often more valuable than perfectly DRY code.

3. When Dealing with Similar but Fundamentally Different Concepts

Just because two pieces of code look similar doesn't mean they represent the same concept. For example:

• Two functions that happen to have similar implementations today might evolve differently tomorrow
• UI components that look identical now might need to diverge for accessibility or localization reasons
• Business logic that appears duplicated might actually represent different domain concepts

Sign to watch for: If you find yourself adding conditional logic or flags to a shared component to handle different use cases, it might be time to split them up.

4. When Performance Is Critical

In performance-critical sections of your code, some duplication might be preferable to:

• Additional function call overhead
• Unnecessary abstraction layers
• Generic solutions that can't be optimized as well as specialized ones

This is particularly relevant in game development, embedded systems, and high-frequency trading applications.

5. When Working with Third-Party Code

When integrating with external libraries or APIs, you might need to repeat certain patterns that are specific to that integration. Trying to DRY these might:

• Create tight coupling to third-party implementations
• Make it harder to replace the dependency later
• Obscure the fact that you're working with an external system

6. During Rapid Prototyping

In early stages of development when requirements are unclear and changing rapidly:

• Spending time on perfect DRYness can slow you down
• You might abstract the wrong things
• The code will likely change anyway

It's often better to move fast first, then refactor to DRY once patterns stabilize.

7. When Domain Experts Prefer Some Repetition

In some domains (like legal contracts, scientific formulas, or regulatory documentation), repetition serves an important purpose:

• It makes each section self-contained
• It prevents misinterpretation when sections are viewed in isolation
• It accommodates domain experts who expect certain patterns

8. In Configuration and Deployment Scripts

Configuration files and deployment scripts often benefit from being explicit rather than DRY:

• Each environment might need slightly different settings
• Explicit configurations are easier to debug
• The cognitive load of understanding abstractions often outweighs the benefit

Conclusion

The DRY principle is incredibly valuable, but like all principles, it's a guideline rather than an absolute rule. Good engineering judgment involves knowing when to apply DRY and when to accept some duplication for higher priorities like clarity, flexibility, or performance. The key is to be intentional - if you're choosing to duplicate code, do so for good reasons, not out of laziness. And remember, you can always refactor to DRY later when the right abstraction becomes clear.