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dev.typeparams: type checker does not allow to use receive operation even all types in type list are channels #43671

tdakkota opened this issue Jan 13, 2021 · 2 comments


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@tdakkota tdakkota commented Jan 13, 2021

What version of Go are you using (go version)?

$ go version
go version devel +f065ff221b Tue Jan 12 15:56:55 2021 -0800 windows/amd64

Does this issue reproduce with the latest release?


What operating system and processor architecture are you using (go env)?

  • windows/amd64
  • go2go playground

What did you do?
Also, I got same result from dev.typeparams typechecker using

$ go tool compile -G ./example.go

The problem is here

case syntax.Recv:
typ := x.typ.Chan()
if typ == nil {
check.invalidOpf(x, "cannot receive from non-channel %s", x)
x.mode = invalid
if typ.dir == SendOnly {
check.invalidOpf(x, "cannot receive from send-only channel %s", x)
x.mode = invalid
x.mode = commaok
x.typ = typ.elem
check.hasCallOrRecv = true

x.typ.Chan() returns nil if x.typ is a *TypeParam.

What did you expect to see?

Successful type-check or a stub error like generic slice expressions not yet implemented. All types in RecvChan[T] type list support receive operation.

What did you see instead?

An error

invalid operation: cannot receive from non-channel ch (variable of type parameter type C)
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@tdakkota tdakkota commented Jan 13, 2021

@griesemer griesemer self-assigned this Jan 13, 2021
@griesemer griesemer added this to the Go1.17 milestone Jan 13, 2021
@griesemer griesemer added the NeedsFix label Jan 13, 2021
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@griesemer griesemer commented Jan 13, 2021

This has not yet been implemented.

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