Dependency inversion principle

Also called: DIP

The D in SOLID: business code defines the interfaces it needs, and details like databases and vendors implement them.

Definition

High-level code should not depend on low-level details; both should depend on an abstraction owned by the high-level side. At runtime checkout still calls the payment provider, but in the source code the provider's adapter depends on checkout's PaymentGateway interface, not the other way round. Dependency injection is a common way to supply the implementations.

In practice

CheckoutService asks for a PaymentGateway; a StripeGateway class in the infrastructure layer implements it.

Learn it in context

Lessons that use this term.

SOLID PrinciplesPatterns

Related terms

Dependency injectionGiving an object the things it needs from outside, instead of letting it create them itself.
Inversion of controlA design where a framework creates your objects and calls your code, instead of your code creating everything and calling the framework.