Interfaces are not equal: "m2() aer" and "m2() ber" has different return 
type. Even compiler told you about it.
On Monday, May 24, 2021 at 9:20:51 AM UTC+3 Amnon wrote:

> See https://play.golang.org/p/5x9JrD55WKc
>
> The interfaces aer and ber look equivalent.
> Both contain a function which returns nothing called m1
> and a function which returns another an instance of the interface m2.
>
> If we comment out m2, then the code will compile.
> But otherwise we get an error:
>
> ./prog.go:14:5: cannot use a (type aer) as type ber in argument to bar: 
> aer does not implement ber (wrong type for m2 method) have m2() aer want 
> m2() ber 
>
> even though aer and ber should be equivalent!
>
> package main
>
> type aer interface {
> m1()
> m2() aer
> }
>
> type ber interface {
> m1()
> m2() ber
> }
>
> func Foo(a aer) {
> bar(a)
> }
>
> func bar(b ber) {
> }
>
> func main() {
> }
>
>

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