Golang interface union type parameter

Richiise Nugraha

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Mar 12, 2022, 11:57:35 AM3/12/22

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Is Go type parameter supports interface union?

My case

type MessageSpec interface { MessageA | MessageB }
type MessageA interface { ID() uint64 }
type MessageB interface { Uid() uint64 }

but got compile error:

./prog.go:14:2: cannot use main.MessageA in union (main.MessageA contains methods) ./prog.go:14:13: cannot use main.MessageB in union (main.MessageB contains methods)

I tried to look for documentation and readed https://go.googlesource.com/proposal/+/refs/heads/master/design/43651-type-parameters.md#interface-types-in-union-elements

There's example

> type Stringish interface { string | fmt.Stringer }

but it also throwing error

> ./prog.go:19:11: cannot use fmt.Stringer in union (fmt.Stringer contains methods)

Is this a bug? i know my case is not the same thing as like the one i referenced from the proposal

but it is throwing the same error.

Thanks

Richiise Nugraha

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Mar 12, 2022, 12:14:22 PM3/12/22

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https://go.dev/play/p/SgTiaeE9J2b?v=gotip

Richiise Nugraha

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Mar 12, 2022, 12:22:53 PM3/12/22

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OK seems i already got the answer
https://github.com/golang/go/issues/45346#issuecomment-862505803
https://github.com/golang/go/issues/49054

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