Interactors

An interactor is a software component that encapsulates the execution of a specific use case, implementing the application's business rules and coordinating the flow of data between the user interface, data stores, and domain entities. In many modern architectures, including Clean Architecture and VIPER, the interactor is the implementation of a use case and sits between the UI layer and the data/domain layers.

Typically, an interactor receives input from the presentation layer through a request or input boundary, validates and applies business rules, delegates data retrieval and persistence to gateways or repositories, and constructs a result to be delivered to the presentation layer through an output boundary or presenter. It should remain independent of UI details and framework concerns, enabling straightforward testing.

Interactors are often designed to be stateless with respect to a single use-case invocation, though some use cases may retain session-like state during the execution. They rely on domain entities to enforce invariants, and on gateways or repositories to interact with persistence or external services. By separating orchestration from UI and data access, interactors help maintain separation of concerns and improve testability.

Terminology varies by framework. The term "use-case interactor" or "application service" is common, and in VIPER the interactor focuses on business logic while presenters handle presentation formatting. Outside software architecture, "interactor" can be used more generally to refer to any component that participates in an interaction between a system and a user or other systems, but in most technical contexts it denotes the use-case implementation.