If you assign a value to an interface, it will get copied. That's the same as if you assign an int to another int - it will get copied. If you want the interface to contain a reference, you have to assign a pointer to it: https://go.dev/play/p/nLw51pjWh4u
Side note: Go doesn't have "instances". It has "variables", which is *probably* what you mean. On Fri, Nov 25, 2022 at 10:55 AM Denis P <denis.puj...@gmail.com> wrote: > Thank you everyone for your help. > The problem still exists. > I am looking for a solution where s and s2 point to the same instance. > The current example proves they are different instances. > https://go.dev/play/p/_JyfJelhIy4 > > The main goal is to store any type in a wrapper and then get the reference > of the actual struct. > Also it must be the same instance, so the println should print 2, 2, 2 > > But look like there is no obvious solution. :-( > > On Friday, 25 November 2022 at 08:19:17 UTC Brian Candler wrote: > >> To give a real-world example: >> >> https://pkg.go.dev/github.com/prometheus/client_golang/prometheus >> >> type metrics struct { >> cpuTemp prometheus.Gauge >> hdFailures *prometheus.CounterVec >> } >> >> Question: why is prometheus.Gauge not a pointer, but >> *prometheus.CounterVec is a pointer? >> >> Answer: because prometheus.Gauge is an interface, whereas >> prometheus.CounterVec is a struct. >> >> An interface essentially already *contains* a pointer to a data value - >> in fact, a tuple of (type, pointer). So you should never take a pointer to >> an interface. Just pass the interface value, and it will copy the (type, >> pointer) pair. >> >> However, when you extract a value from an interface, it *will* always >> copy the internal value. This avoids aliasing issues: someone who passes >> an interface value to someone else, won't expect the recipient to be able >> to change the sender's copy. >> >> e.g. >> https://go.dev/play/p/u5y3Kwm9Ydz >> >> Of course, if your interface *contains* a pointer, then the recipient of >> the interface can modify the thing being pointed to. >> https://go.dev/play/p/o_XAJtNuyGF >> >> But they can't modify the pointer itself held within the interface, to >> make it point to something else. >> >> The short version is: avoid pointers to interfaces, as the FAQ says. >> Instead, let a concrete pointer value satisfy an interface. >> >> On Friday, 25 November 2022 at 07:40:59 UTC Nigel Tao wrote: >> >>> Possibly relevant: >>> https://go.dev/doc/faq#pointer_to_interface >>> >> -- > 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/948dc8f3-385e-4f50-a44b-ddf4792e6362n%40googlegroups.com > <https://groups.google.com/d/msgid/golang-nuts/948dc8f3-385e-4f50-a44b-ddf4792e6362n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- 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/CAEkBMfE7XX%2BnHJTW36GaoLjQWidY7GCjpHP1zyOJJzMcSq13JA%40mail.gmail.com.
