dependency-inversion-principle

Reduce tight coupling by applying dependency inversion to prevent classes from instantiating their own dependencies. Define interfaces for external services and use constructor injection to wire abstractions, enabling easy swapping and decoupled implementations.

Mock external services during unit testing by converting concrete dependencies to interface abstractions. Inject these interfaces via constructors so tests can easily substitute real services like EmailService or UserRepository with mock implementations.

Constructor injection improves testability and modularity by forcing high-level modules to depend on interfaces rather than concrete classes. This allows you to easily mock or replace services during tests and swap providers without modifying core logic.

Wire implementations at a composition root when applying dependency inversion. This central location handles mapping interfaces to concrete classes, ensuring high-level modules never instantiate external services or utilities directly themselves.

Refactor a class to use interfaces instead of concrete dependencies when you need to swap providers, improve modular architecture, or enable unit tests without real external services. This prevents high-level modules from creating their own dependencies.

Yes, dependency inversion lets you swap utilities and repositories without modifying high-level modules. By enforcing interface abstractions and constructor injection, implementations can be replaced at the composition root without impacting dependent classes.