proposal: x/sync/singleflight: add generic API

[catatsuy]

• singleflight is a great library, but the return value of the argument function uses interface{}. If you use generics, you can make it a flexible function by simply passing a type.
• For compatibility, define it with a different name than singleflight.Group, e.g. singleflight.GroupGenerics.
• singleflight.GroupGenerics has exported functions Do(), DoChan() and Forget() as well as singleflight.
  • singleflight.GroupGenerics has the following types, arguments, and return values.

type GroupGenerics[V any] struct {
	mu sync.Mutex          // protects m
	m  map[string]*call[V] // lazily initialized
}

func (g *GroupGenerics[V]) Do(key string, fn func() (V, error)) (v V, err error, shared bool)
func (g *GroupGenerics[V]) DoChan(key string, fn func() (V, error)) <-chan Result
func (g *GroupGenerics[V]) Forget(key string)

I changed the existing API to try it out. Please refer to it.

https://github.com/catatsuy/sync/pull/1/files

[ianlancetaylor]

Please include the new API with docs (but without the implementation) in this issue. That makes it a easier for people to see the API being proposed. Thanks.

[catatsuy]

@ianlancetaylor Sorry for the late reply. I have changed my description. Could you confirm it?

[ianlancetaylor]

Thanks. I hope that we can find a better name than GroupGenerics.

[catatsuy]

I think so, too. GroupGenerics does not represent the role. We are looking for the good ideas.