Thanks for the reply. Is there any specific use case that this intended behavior is supposed to solve? It appears to me that it is just a case of simplistic implementation where Go does not look deep enough to see if any dependent interfaces are identical. In this case, Go does not bother to look beyond Formatter interface in order to conclude whether FormatterA and FormatterB are identical. In here, I define 'identical' as being interchangeable, rather than semantic equality. So when I refer to TypeA and TypeB as identical, it means you can use TypeA in place of TypeB, and vice versa.
Back to the actual situation, Package A and Package B are developed in tandem by different teams. They have some communication on how their components will interact with each other and fit the bigger picture. They use interface to define contracts that are required in order for their components to work. Since Go interface is implicit, this is supposed to work fine. As an example, if I were to reduce the prior example as follows, it works fine. (Link to the playground: https://play.golang.org/p/zrpjSYTIyxZ) import ( "fmt" ) func main() { str := MyString("Hello world!") Print(str) strA:=StringerA(str) Print(strA) } type StringerA interface { String() string } type StringerB interface { String() string } type MyString string func (s MyString) String() string { return string(s) } func Print(s StringerB) { fmt.Println(s.String()) } However, when I add a more complex interface, as in the first example involving Formatter, it breaks. Go fails to recognize that FormatterA and FormatterB are interchangeable despite the facts that their dependencies (StringerA and StringerB) are interchangeable. Visually, the components should look like this: [image: go.png] Let me know what you think. Thanks. Henry On Saturday, May 25, 2019 at 1:54:11 AM UTC+7, Wagner Riffel wrote: > > It's not a bug, FormatterA and FormatterB method has different > signatures, they are not identical, one wants Format(StringerA) other > Format(StringerB), thus your Format type only implements FormatterA > but Print wants a FormatterB. > -- 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/3280cda6-ba3e-4847-a23e-5b1c6d5128be%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
