Basically you almost never want pointer-to-interface in practice. The temptation is to have a struct which satisfies your interface, and then you end up with thinking you want pointer-to-interface.
Instead, make pointer-to-struct satisfy the interface, and then you don't need pointer-to-interface any more. On Thu, Aug 30, 2018 at 10:34 AM Eric Raymond <e...@thyrsus.com> wrote: > > > On Thursday, August 30, 2018 at 1:14:25 PM UTC-4, Jan Mercl wrote: > >> On Thu, Aug 30, 2018, 18:57 Eric Raymond <e...@thyrsus.com> wrote: >> >>> I'm trying to translate this to Go in a type-safe way. To do this, I >>> need to be able to write two declarations: "Slice of pointers to objects >>> satisfying the Event interface" >>> >> >> []*Event, but quite probably []Event is what is really needed. >> >> and "map of string keys to pointers to objects satisfying the Event >>> interface". >>> >> >> map[string]*Event, but once again, my bet is on map[string]Event. >> >> My attempts so far have yielded very cryptic error messages and no >>> success. >>> >> >> It would probably help your case if you could provide some self-contained >> example reproducing the errors and post a link to the Go Playground. >> > > That's hard. The structures are intertwingled parts of ab only partly > translated 14KLOC program But I can isolate some key declarations. If > Event is my interface type, and I write > > events []Event > _mark_to_object map[string]*Event > > as member declarations in the Repository class, and b is a pointer to a > just-allocated instance of a Blob object satisfying the Event interface, > and I write this > > b.repo._mark_to_object[mark] = b > > I get this message: > > cannot use b (type *Blob) as type *Event in assignment: > *Event is pointer to interface, not interface > > Note that the map values really do need to be pointers, because I need the > map to refer to the mutable data in the event list, not a local copy of it > in the map. What's stumping me is how to communicate this to the compiler. > > -- > 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. > For more options, visit https://groups.google.com/d/optout. > -- 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. For more options, visit https://groups.google.com/d/optout.
