I'm confused about the constructors in Go. Most constructors I've seen return a struct, but 'Effective Go' suggests that an interface can be returned in some cases, according to the rule of 'Generality'.
I trust 'Effective Go' to provide good ideas, but this doesn't seem to follow the principle of 'accept interfaces, return structs'. I guess that many types implement an interface and nothing more than that, so in that case it would be common to see constructors which return interfaces.
Another related statement is that interfaces should be defined by the consumer, but 'Generality' means that the interface is defined by the producer.
Can someone clarify?