On Thu, Aug 27, 2020 at 3:53 AM targe...@gmail.com <target....@gmail.com> wrote: > > Please don't forget that interface pointer isn't simple. It's a so-called > "fat pointer" which consists of pointer to data and pointer to methods table. > Thus, we have 4 potential states - (nil, nil), (nil, pointer), (pointer, nil) > and (pointer,pointer). First one is just ordinary nil interface. Last one is > just ordinary interface pointer with all operations callable without issue > (as long as they're properly implemented, of course). Third one with valid > data pointer and nil table pointer can be AFAIK created only through > reflection and is safely considered "invalid state". We're left with second > state with nil data pointer and valid table pointer, making interface methods > callable on it. It wouldn't be a problem - if such state couldn't be created > by merely casting typed nil pointer (typed pointer variable with nil value) > to interface. Why is this an issue? Because most interface implementations > require valid data pointer. "Static" (i.e. not needing data) implementations > can be considered corner case.
Other people have said this too, but I want to emphasize that there are not 4 potential states of an interface value. There are 2 potential states: 1) interface does not hold any value, and is == nil; 2) interface holds a value, and is != nil. When you start talking about an interface as a fat pointer you are talking about how those 2 states are implemented. There are other possible implementations, and in fact the implementation in gccgo used to be different. And even the implementation in the gc compiler has changed; at one time ints and other small values were stored directly in the interface value, but now we instead store a pointer to the data. Ian -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAOyqgcWGy7nGqxbR9Gicf0owUB_eJWre0fTDzuUcX1yFNOO69A%40mail.gmail.com.
