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cmd/compile: a little inconsistency on uses of type parameters in type parameter lists #51499

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go101 opened this issue Mar 5, 2022 · 2 comments
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@go101
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@go101 go101 commented Mar 5, 2022

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

$ go version
go version go1.18rc1 linux/amd64

What did you do?

type C1[T []T] struct{} // okay
type C2[T *T] struct{}  // error: undefined: T

What did you expect to see?

Both compiles.

What did you see instead?

The second one doesn't compile.

Not sure if this is intended, just feel they should be consistent.

@ianlancetaylor
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@ianlancetaylor ianlancetaylor commented Mar 5, 2022

CC @griesemer

For 1.19.

@ianlancetaylor ianlancetaylor added the NeedsInvestigation label Mar 5, 2022
@ianlancetaylor ianlancetaylor added this to the Go1.19 milestone Mar 5, 2022
@griesemer
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@griesemer griesemer commented Mar 5, 2022

This is working correctly according to the spec. The C2 type parameter list is ambiguous and per the spec it is parsed as an (invalid) array declaration since T is unknown. These work:

type C2[T *T,] struct{}
type C3[T interface{*T}] struct{}

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