Software/Engineering/Principle/DRY

• Don't Repeat Yourself (DRY)

  • Definition

    • DRY is a software development principle that states "Every piece of knowledge must have a single, unambiguous, authoritative representation within a system"
    • The principle was first introduced by Andy Hunt and Dave Thomas in their book "The Pragmatic Programmer"

  • Core Concept

    • Single Source of Truth: Each piece of knowledge should exist in only one place
    • Avoid Duplication: Don't copy code, data, or logic across multiple locations
    • Maintain Consistency: Changes to shared knowledge should propagate automatically

  • Benefits

    • Reduced Maintenance: Changes only need to be made in one place
    • Consistency: Eliminates inconsistencies that arise from duplicate code
    • Easier Debugging: Issues are easier to trace when logic exists in one location
    • Improved Reliability: Less chance of bugs from forgetting to update duplicates

  • Common Violations

    • Copy-Paste Programming: Duplicating code blocks across functions or files
    • Magic Numbers/Strings: Hard-coding the same values in multiple places
    • Duplicate Business Logic: Implementing the same rules in different parts of the system
    • Repeated Configuration: Same settings defined in multiple configuration files

  • Implementation Strategies

    • Functions and Methods: Extract common logic into reusable functions
    • Constants and Enums: Define shared values in a single location
    • Configuration Management: Centralize configuration in one place
    • Templates and Inheritance: Use design patterns to avoid code duplication
    • Libraries and Modules: Create reusable components for common functionality

  • Related Principles

    • Software/Engineering/Principle/SOLID: Single Responsibility Principle aligns with DRY
    • Software/Engineering/Principle/KISS: Keep It Simple, Stupid - DRY helps maintain simplicity
    • Software/Engineering/Principle/YAGNI: You Aren't Gonna Need It - Balance DRY with over-engineering

  • Caveats and Considerations

    • Over-Abstraction: Don't create unnecessary abstractions just to avoid duplication
    • Premature Optimization: Sometimes duplication is acceptable for clarity or simplicity
    • Context Matters: What constitutes "knowledge" can vary by context
    • Balance with Other Principles: DRY should be balanced with maintainability and readability