Fundamental Principles of Software Development: DRY, KISS, YAGNI, POLS, and CoC

Fundamental Principles of Software Development: DRY, KISS, YAGNI, POLS, and CoC

Software development is a complex process requiring balance between principles like DRY (Don’t Repeat Yourself), KISS (Keep It Simple, Stupid), YAGNI (You Ain’t Gonna Need It), POLS (Principle of Least Surprise), and CoC (Convention over Configuration). These principles guide developers to build maintainable, readable, and scalable systems while avoiding over-engineering and unnecessary complexity.

Key Themes and Explanations

1. DRY (Don’t Repeat Yourself)

• Purpose: Eliminate redundant knowledge representation to avoid coupling and maintain domain clarity.
• Impact: Improves maintainability but risks over-abstraction if misapplied.
• Example:
  • Misapplication: Merging two distinct domain validations (e.g., billing vs. shipping) into a single ValidarEndereco() function introduces unintended coupling.
  • Correct Approach: Keep domain-specific validations separate (ValidarEnderecoDeCobranca, validarEnderecoDeEntrega) and share neutral utilities (e.g., CEP normalization).

2. KISS (Keep It Simple, Stupid)

• Purpose: Prioritize simplicity to reduce technical debt and improve readability.
• Impact: Simplicity is not about brevity but clarity. Overuse of patterns can lead to over-engineering.
• Example:
  • Misapplication: Using complex design patterns (e.g., MVC) for trivial tasks.
  • Correct Approach: Start with minimal viable code and evolve it with patterns only when complexity justifies it.

3. YAGNI (You Ain’t Gonna Need It)

• Purpose: Avoid speculative features or abstractions not required by current needs.
• Impact: Reduces unnecessary complexity and maintenance costs.
• Example:
  • Misapplication: Building an internationalization framework for a Portuguese-only app.
  • Correct Approach: Implement features only when explicitly needed, avoiding premature abstractions.

4. POLS (Principle of Least Surprise)

• Purpose: Ensure code behavior aligns with expectations, minimizing hidden side effects.
• Impact: Improves predictability and reduces debugging time.
• Example:
  • Violation: A calcularTotal() function that modifies the cart state (e.g., applying discounts) without explicit intent.
  • Correct Approach: Separate concerns (e.g., getSubtotal() and aplicarDescontos()).

5. CoC (Convention over Configuration)

• Purpose: Reduce configuration overhead by enforcing standardized conventions.
• Impact: Accelerates development and enforces consistency across teams.
• Example:
  • Without CoC: Manually mapping routes and controllers in Express.
  • With CoC (AdonisJS): Automatically resolves ProductsController.index() based on naming conventions.

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Working Example (CoC in AdonisJS)

// app/Controllers/Http/ProductsController.ts
import type { HttpContextContract } from '@ioc:Adonis/Core/HttpContext'

export default class ProductsController {
  public async index({ response }: HttpContextContract) {
    const products = [
      { id: 1, name: 'Teclado Mecânico' },
      { id: 2, name: 'Monitor Ultrawide' },
    ]
    return response.json(products)
  }
}

Command to Generate Controller:

node ace make:controller Product

This command automatically creates the controller in app/Controllers/Http/ProductsController.ts with the index method, adhering to naming and structure conventions.

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Recommendations

• Use DRY judiciously: Avoid merging distinct domain logic; share utilities instead.
• Apply KISS iteratively: Start simple and refactor only when complexity arises.
• Follow YAGNI strictly: Implement features only when required, not speculated.
• Adhere to POLS: Ensure functions do one thing and do it predictably.
• Leverage CoC for scalability: Use frameworks like AdonisJS to reduce boilerplate and enforce consistency.

Common Pitfalls:

• Overusing DRY to create overly abstracted systems.
• Confusing simplicity (KISS) with minimal code.
• Prematurely applying YAGNI to avoid future work, leading to rigid designs.
• Ignoring POLS, resulting in functions with hidden side effects.
• Forgetting to define clear conventions in CoC, leading to inconsistency.

For further reading: Princípios fundamentais do desenvolvimento de software