golang-structs-interfaces

Design Go structs and interfaces for maintainability by keeping interfaces small and composable, accepting interfaces as inputs, returning concrete structs from constructors, and using consistent receiver semantics to ensure clear, testable code.

Compose larger Go interfaces by embedding smaller 1–3 method interfaces. This approach keeps contracts small and composable, which makes mocking easier and improves reasoning in complex services.

Go constructors should return concrete struct types, not interfaces. Returning concrete types allows direct field and method access, while accepting interfaces for inputs enables flexible mocking and dependency injection.

Use type assertions and type switches in Go to handle dynamic values safely. Apply compile-time interface checks and safe comma-ok assertions to perform optional capability checks without risking runtime panics.

Use struct embedding in Go to promote a full "is-a" API surface, and use named fields to keep "has-a" dependencies internal. Embedding exposes methods directly, while named fields restrict access to the containing struct.

Avoiding premature interfaces in Go prevents unnecessary abstractions that complicate code. Define interfaces only for consumed dependencies to support dependency injection and mocking, keeping the codebase clear and composable as systems grow.