On Fri, Feb 11, 2022 at 12:51 PM Kamil Ziemian <kziemian...@gmail.com>
wrote:
> Can someone explain me, why compiler can't throw an error when it find
> unused type parameter? I like that in Go unused variable, or import, is
> compile time error and I would appreciate the same behavior with unused
> type parameters.
>
I'm not sure it's reason enough, but I do have a case where I want to have
unused type-parameters on a type.
Essentially, I have
type ID string
func Call(ctx context.Context, id ID, req Message) (Message, error)
which does an RPC-like call. It's used as
r, err := framework.Call(ctx, somepkg.ID, somepkg,Request{…})
resp := r.(somepkg.Response)
With generics, this would be
type ID string
func Call[Req, Resp Message](context.Context, ID, Req) (Resp, error)
But this requires writing
resp, err := framework.Call[somepkg.Request, somepkg.Response](ctx,
somepkg.ID, somepkg.Request{…})
as return types can't be inferred. Instead, I plan to do
type ID[Req, Resp Message] string // unused type-parameters
func Call[Req, Resp Message](context.Context, ID[Req, Resp], Req) (Resp,
error)
which allows `somepkg` to declare
var ID = framework.ID[MyRequest, MyResponse]("my-name")
letting the client write
resp, err := framework.Call(ctx, somepkg.ID, somepkg.Request)
Now somepkg.ID carries both types and is in an argument, so both types can
be inferred.
As I said, I'm not 100% yet on whether this is a good idea and much less if
that would be enough reason to keep allowing unused type parameters. But
there is at least some potential benefit to allowing it.
>
> I need to go for a while, I will go back with more questions about what
> you can get when using "[]" in Go.
>
> Best,
> Kamil
>
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