Generics

[Jérôme LAFORGE]

Hello,

I do some tests with generics with Go 1.18.

But I can't reach my goal.

With https://go.dev/play/p/7kxMEWtXcPG

I have:

```

panic: json: Unmarshal(nil *main.payload)

goroutine 1 [running]:
main.main()
	/tmp/sandbox3884661607/prog.go:43 +0x112

Program exited.
```

Because payload (line 15) is nil

Any tips ?

Many thx.

[Martin Schnabel]

how about https://go.dev/play/p/YXOTLKpvXNI using json unmarshal
directly and without using binary marshaller.

or even https://go.dev/play/p/GFE3rnyx9f8 without the endpoint abstraction.

or maybe explain what you want to achieve other than unmarshalling a
json payload?

best regards

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[Martin Schnabel]

the reason your snippet does not work is that you pass in *payload as T
and the zero value of a pointer type is nil and json unmarshal cannot
with nil pointer values. so would need to pass in payload as T and
*payload as P and somehow explain that P is *T and a
encoding.BinaryUnmarshaler. I am not versed enough in go generics to
know the solution, but would propose to take a simpler approach if possible.

[Sebastien Binet]

what you may be looking at is (in the words of Rog Peppe) "structural
type constraints":

https://go.dev/play/p/HiFc9CUfI7P

-s

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[Jérôme LAFORGE]

I use binary marshaller interface because payload is not encoded into json only (xml, binary or whatever).

I have already classic solution that works but I just want to test in order to see how generics can impact it.

[Jérôme LAFORGE]

Thanks Sebastien