The posted diagram isn't correct. Updated the diagram with the new one. [image: go1.png]
On Saturday, May 25, 2019 at 10:38:42 AM UTC+7, Henry wrote: > > 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/86e27716-0dbc-42bd-9c81-45243988c3b5%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
