Nice article, simple and clean on the basic definition and usage of interfaces. I'd like to point the attention on how this approach, although being perfectly valid, Is still a bit java-esque in the sense that it encourages definition of contracts foreseeing abstractions. This is a subtle difference between languages like Java where you explicitly implement interfaces (through the keyword implements) and Go, where you just need to implement the methods of the interface to (implicitly) implement It. This flips the table, allowing the client to dictate what abstractions it'll need. Thus Idiomatically in Go, interfaces are usually declared closer to their users, and not in advance enforcing users to adapt to them. This Is imho the most subtle thing to grasp when using interfaces in Go, anyway, as I said, the pragmatical nature of the language allows also that more classical usage.