This is a result of the assignability requirement of the spec: https://golang.org/ref/spec#Comparison_operators In this particular case, IAB is assignable to IA, so it's a valid comparison: https://golang.org/ref/spec#Assignability ("T is an interface type and x implements T" -- a value of type IA implements IAB and IAC) But IAC is not assignable to IAB or vice versa. Thus the comparison is not valid.
So, no, I don't think it's an entirely intentional effect, but a side-effect of the assignability-requirement. Using assignability as a requirement for comparisons instead of type-equality makes some things more convenient. And that IAC isn't assignable to IAB or vice versa makes total sense. On Sun, Jul 31, 2016 at 6:23 PM, T L <tapir....@gmail.com> wrote: > > > On Sunday, July 31, 2016 at 11:46:28 PM UTC+8, bradfitz wrote: >> >> Interface values are comparable. If they have different concrete types, >> they compare to false. >> >> See https://golang.org/ref/spec#Comparison_operators >> > > I mean this: > >> package main >> >> import "fmt" >> >> type IA interface { >> A() >> } >> >> type IAB interface { >> A() >> B() >> } >> >> type IAC interface { >> A() >> C() >> } >> >> type T struct{} >> func (t T) A(){} >> func (t T) B(){} >> func (t T) C(){} >> >> func main() { >> var t T >> var a IA = t >> var ab IAB = t >> var ac IAC = t >> >> fmt.Println(a == ab) // true >> fmt.Println(ac == ab) // error: mismatched types IAC and IAB >> } >> > > >> >> >> On Sat, Jul 30, 2016 at 10:33 PM, T L <tapi...@gmail.com> wrote: >> >>> Is it essential? >>> >>> -- >>> 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...@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. > -- 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.
