| 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
