proposal: x/sync/singleflight: add generic version

[bradfitz]

The singleflight package's Group type uses string keys and interface{} values:

https://pkg.go.dev/golang.org/x/sync/singleflight#Group

I've locally forked it to add generics [K comparable, V any] but I'd like to get it upstream instead.

Proposal: add singleflight.TypedGroup[K, V] or singleflight.GenericGroup[K, V] or singleflight.GroupOf[K, V] behind a go1.18 build tag.

Do we have a convention yet on naming new parallel generic types alongside others?

Related: #47657 (for PoolOf, MapOf). (There was also talk of default type parameters so old code could instantiate types and get the old behavior (in this case [string, any]) and new callers could specify types?)

[ianlancetaylor]

I don't think we have a convention yet.

[icholy]

What about x/sync/v2/singleflight ?

[catatsuy]

I tried it before. Thank you.

refs: #52520

[gopherbot]

Change https://go.dev/cl/425187 mentions this issue: all: switch singleflight to use generic