Designing for Composability

The type system is what lets Dagger workflows keep going. A well-typed result can be passed to another function, another module, a generated client, a check, a generator, or an agent.

Composable Return Values

Return values should help the caller continue the workflow:

• Return Container when the caller may still run, publish, export, or inspect it.
• Return Directory or File when the caller needs artifacts.
• Return Service when another step needs a live endpoint.
• Return Changeset when the module proposes source edits.
• Return a user-defined object when the caller needs a domain concept with more methods.

Avoid Dead Ends

Strings and logs can be useful final outputs, but they are often dead ends. If a caller has to parse text to continue, the module probably returned too little structure.

Composition Across Modules

Design return types so other modules can consume them without knowing implementation details. This is where type design and interface design meet.

TODO: Cross-link this chapter with Interfaces and Composition after the interface guide is expanded.