On Sun, Jul 3, 2016 at 12:27 PM, Jon Bodner <j...@bodnerfamily.com> wrote: > > I'm working on a DAO adapter layer helper called Proteus > (https://github.com/jonbodner/proteus), and ran into an interesting quirk in > what Go considers equivalent interfaces. I recreated a simplified version of > the issue is at https://play.golang.org/p/BS3-bUKtO9 . > > The code that I linked does not compile, with the error: > > V does not implement CalcB (wrong type for Calculate method) > have Calculate(int) ResultA > want Calculate(int) ResultB > > > ResultA and ResultB are identical interfaces; both define a single method > Result that takes in no parameters and return an int. > > However, if I put in a wrapper around V, I can get it to work: > https://play.golang.org/p/XUoZwsBaFn > > What I don't understand is that the wrapper doesn't do any casting of > ResultA to ResultB, and that's OK in this situation. But the Go compiler > can't figure out that ResultA and ResultB are identical without that > wrapper. Why is that? Why does the compiler fail the first case and pass the > second one?
ResultA and ResultB are assignable but not identical. https://golang.org/ref/spec#Type_identity https://golang.org/ref/spec#Assignability For the specific case of interface types, you may be interested in https://golang.org/issue/16209 . 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. For more options, visit https://groups.google.com/d/optout.
