If you create a wrapper interface type and create *generic constraints* with the *MyWrapper* struct then it'll type cast with *interface* with *(T)*.
https://go.dev/play/p/-VnQxG77sDL On Fri, Nov 25, 2022 at 3:38 PM 'Axel Wagner' via golang-nuts < golang-nuts@googlegroups.com> wrote: > 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 > <https://groups.google.com/d/msgid/golang-nuts/CAEkBMfE7XX%2BnHJTW36GaoLjQWidY7GCjpHP1zyOJJzMcSq13JA%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- Thanks & Regards Deeptiman Pattnaik -- 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/CAAWK-epK544zJnjnJff99sA%3DbJiKOPftv_3ydgOsaRqo38Ch%2Bw%40mail.gmail.com.
