golang-structs-interfaces

Designing Go structs and interfaces for safe composition requires keeping interfaces small with 1–3 methods, defining them at the consumer package, returning concrete types from constructors, and accepting interface parameters to ensure composability and maintainability.

The best way to use type assertions in Go without causing runtime panics is to use the comma-ok idiom or type switches, which safely check optional capabilities and handle failed assertions gracefully without crashing the program.

Use struct embedding in Go when you want to promote the full inner API to create an "is a" relationship, and use named fields for a "has a" relationship when you want to encapsulate the inner type without exposing its entire method set.

To make the zero value of a Go struct useful, design your struct fields so their default initialized state is immediately safe and operational without requiring explicit constructor calls, and add a noCopy sentinel to prevent accidental unsafe struct copies.

Go constructors should return concrete types instead of interfaces to preserve type clarity and allow callers to access concrete type methods, while accepting interfaces as parameters preserves dependency injection flexibility and simplifies testing.

Dependency injection in Go often uses interface type assertions to check for optional behaviors, allowing consumers to dynamically verify if an injected dependency supports specific capabilities before attempting to invoke those methods.