typescript-solid

name	typescript-solid
description	SOLID principles for reducing coupling and improving testability—SRP, OCP, LSP, ISP, and DIP with TypeScript examples.
triggers	["SOLID","SRP","OCP","LSP","ISP","DIP","single responsibility principle","open-closed principle","Liskov substitution","interface segregation","dependency inversion","god class","fat interface","one reason to change","extend without modifying","depend on abstractions","interface too large","reduce coupling","improve testability"]

SOLID Principles

Quick Reference

Principle	Rule	Signal it's violated
SRP — Single Responsibility	One reason to change	Class handles auth, hashing, and persistence
OCP — Open–Closed	Extend via subclass; don't modify proven code	Adding CSV export requires editing JsonFormatter
LSP — Liskov Substitution	Subtypes substitutable without surprising callers	instanceof checks in calling code; subclass throws "not supported"
ISP — Interface Segregation	Many focused interfaces over one fat one	Read-only client forced to implement write methods
DIP — Dependency Inversion	Depend on abstractions, not concretions	EmailService directly instantiates SendgridClient

Concepts

SRP — One reason to change. Split UserController into UserValidator, PasswordHasher, UserRepository.

OCP — Extend via subclass, don't edit proven code. Add CsvResponseFormatter extends JsonResponseFormatter without touching the base.

LSP — Subtypes must be fully substitutable. ReadOnlyCache extends Cache violating set() is LSP violation—use ReadableCache / WritableCache interfaces instead.

ISP — Split fat interfaces into focused slices. Don't force read-only clients to depend on write methods.

DIP — Depend on abstractions, not concretions. EmailService(transport: MailTransport) not new SendgridClient(). Enables swapping implementations.

→ Full annotated examples for all five principles: references/solid.md