Great intro into how to write nice Go code! One comment regarding interface pollution: While I agree that in many cases it's not needed to introduce an interface, sometimes interfaces help you hide the implementor type: I've now already had it multiple times that I switched from a 'struct implementor' to a 'func type implementor' without breaking compatabilities. Also, by exposing a struct, you also immediately expose that you can create a zero value of that type, which doesn't happen for an interface.