This has to do with how type parameter names are scoped. There have to be
*some* special handling of that, as they can be mutually referential. i.e.
in `func F[T1 any, T2 C[T1]]()`, `T1` must be scoped such that it is
visible for `C[T1]`, which is not a problem regular parameters face.
It is still possible to shadow type parameter names, though, by explicitly
introducing a new scope: https://go.dev/play/p/ooMjxO2REdt?v=gotip
In that way, the problem you observe is similar to shadowing a
function-scoped type declaration, which also doesn't work:
https://go.dev/play/p/QybMkt_yWOh
Either way, this sort of shadowing seems unambiguously bad style. So while
we *may* be able to allow it, as long as there is a clear way around
(namely choosing a different variable name), it seems fine to start with
the more restrictive route, until someone can come up with a good reason to
need to do it.
On Wed, Feb 16, 2022 at 11:45 AM Jochen Voss wrote:
> Dear all,
>
> I stumbled across a difference between type names and type parameter names
> (in the go1.18 beta): I can re-use a type name as a variable name, but the
> same is not possible with type parameter names. Is this difference
> intentional?
>
> For illustration, the following code is valid
> https://go.dev/play/p/r2NAddZmoE3 :
>
> type other int
>
> func test(x other) other {
> other := x + 1
> return other
> }
>
> But this doesn't work https://go.dev/play/p/Dsh9IgvKDDY?v=gotip :
>
> type Numeric interface {
> ~int | ~float64
> }
>
> func test[other Numeric](x other) other {
> other := x + 1
> return other
> }
>
> All the best,
> Jochen
>
>
>
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>
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