design principles

6 posts

SOLID Principles6-part series

SOLID, Actually: Five Rules for Code That Survives Change

SOLID isn't five unrelated rules — it's one idea about managing dependencies and change. Watch one messy NotificationService become clean, one principle at a time.

Asked at Amazon, Google, Microsoft +3

Jul 27, 2026·4 min read

Mediumlow level design oop design principles

Single Responsibility: One Reason to Change, One Owner

SRP isn't 'do one thing' — it's 'answer to one actor'. Watch a Marketing copy tweak break Compliance's audit log, then split one NotificationService by who owns each change.

Asked at Amazon, Google, Microsoft +3

Jul 27, 2026·7 min read

Mediumlow level design oop design principles

Open/Closed: Add a Channel Without Touching the Core

Every new notification channel meant another edit to the same switch — and another regression. Open/Closed makes new behavior a drop-in, not a rewrite.

Asked at Amazon, Google, Microsoft +3

Jul 27, 2026·7 min read

Mediumlow level design oop design principles

Liskov Substitution: If Clients Must Check the Type, You Broke It

An SmsChannel that can't do what a Channel promised isn't a safe stand-in for its base — so callers start type-checking. Liskov, explained simply: a subtype must work anywhere its parent does.

Asked at Amazon, Google, Microsoft +3

Jul 27, 2026·8 min read

Mediumlow level design oop design principles

Interface Segregation: Don't Make Callers Depend on What They Don't Use

One fat Notifier interface forces every channel to stub methods it can't support and every caller to depend on methods it never calls. Interface Segregation splits it into roles.

Asked at Amazon, Google, Microsoft +3

Jul 27, 2026·7 min read

Mediumlow level design oop design principles

Dependency Inversion: Point the Arrow at an Abstraction

A service that news-up its own email sender can't be tested or swapped. Dependency Inversion flips the arrow so high-level policy and low-level detail both depend on an abstraction.

Asked at Amazon, Google, Microsoft +3

Jul 27, 2026·8 min read