Why DRY (Don't Repeat Yourself) in LLD? - Purpose & Use Cases

The Big Idea

What if fixing one bug could fix it everywhere instantly?

The Scenario

Imagine you are building a system where you write the same code or logic in many places to handle user authentication. Every time you need to change the login process, you must find and update all those places manually.

The Problem

This manual approach is slow and risky. You might miss some places, causing bugs. It becomes hard to maintain and update the system. The repeated code wastes time and makes the system fragile.

The Solution

DRY means writing the logic once and reusing it everywhere. This way, you update the code in one place, and all parts of the system benefit. It makes the system cleaner, easier to maintain, and less error-prone.

Before vs After

✗ Before

if user.is_authenticated:
    show_dashboard()
# repeated in many files

✓ After

def check_auth(user):
    return user.is_authenticated

if check_auth(user):
    show_dashboard()

What It Enables

DRY enables building systems that are easier to change, less buggy, and faster to develop.

Real Life Example

Think of a website where the password rules are checked in many places. With DRY, you write the rules once and reuse them, so when rules change, you fix it in one place only.

Key Takeaways

Repeating code causes bugs and wastes time.

DRY means write once, use everywhere.

It makes systems easier to maintain and update.