Software Design Principles Overview

A quick overview of four fundamental principles for writing clean, maintainable, and scalable code: SOLID, DRY, KISS, and YAGNI.

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✅ 1. SOLID Principles

A set of five object-oriented design principles introduced by Robert C. Martin (Uncle Bob):

1. S - Single Responsibility Principle (SRP)
   A class should have only one reason to change.
   ➤ One class = One responsibility.

2. O - Open/Closed Principle (OCP)
   Software entities should be open for extension, but closed for modification.
   ➤ Add new features without modifying existing code (use abstraction and polymorphism).

3. L - Liskov Substitution Principle (LSP)
   Subtypes must be substitutable for their base types.
   ➤ A subclass should behave like its parent class without breaking the program.

4. I - Interface Segregation Principle (ISP)
   Many client-specific interfaces are better than one general-purpose interface.
   ➤ Classes should not be forced to implement methods they don’t use.

5. D - Dependency Inversion Principle (DIP)
   Depend on abstractions, not on concrete implementations.
   ➤ High-level modules shouldn’t depend on low-level ones.

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✅ 2. DRY - Don't Repeat Yourself

"Every piece of knowledge must have a single, unambiguous representation in the system."

• Avoid duplicating code or logic.
• Centralize reusable logic in a single place.

✔️ Good:

function calculateDiscount(price: number) {
  return price > 100 ? price * 0.1 : 0;
}

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✅ 3. KISS - Keep It Simple, Stupid

“Simplicity is key to maintainability.”

• Prefer simple and clear solutions over overly abstract or complex ones.
• Don’t over-engineer unless it’s necessary.

✔️ Good:

function add(a: number, b: number) {
  return a + b;
}

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✅ 4. YAGNI - You Aren’t Gonna Need It

“Don’t implement functionality until it’s actually needed.” • Avoid adding speculative features. • Focus only on the current requirements to keep the codebase lean.

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✨ When combined

• SOLID → Helps structure complex systems.
• DRY → Keeps logic consistent.
• KISS → Avoids unnecessary complexity.
• YAGNI → Prevents writing unused code.