As an appendix, I recommend this article 100go.co/5-interface-..., and the entire book www.manning.com/books/100-go... in general

✨ Testability and Mocking. When the factory function returns the struct, consumers can create their own interfaces based on their specific needs. This makes it easier to mock the behavior for testing since the interface can be narrower and focused on the specific methods the test cares about.

✨ Interface Segregation. Returning the concrete struct allows you to add methods to the struct in the future without breaking backward compatibility. If you return an interface and later need to add a method, all implementations of that interface need to be updated, which can be disruptive.

This decouples the producer from the consumer and avoids forcing a specific abstraction on the user of the handler.

✨ Interfaces Should Be Defined by Consumers. Interfaces are generally more useful when defined by the consuming code rather than the producing code. Returning a concrete struct instead allows the consumer to define and use their own interfaces as needed.

It’s really hard to believe that it’s true 😅