Singleflight with Generics!

Package singleflight provides a duplicate function call suppression mechanism.

A type-safe wrapper around golang.org/x/sync/singleflight that adds generic type support.

• No more type assertions needed in your code:
  • Group[K ~string, V any] - A type-safe version of the original Group.
  • Result[V any] - A generic version of the Result type.
• 100% compatible with the original package, maintaining identical behavior.

Installation

go get pkg.venceslau.dev/singleflight

Usage

Do

Suppress duplicate in-flight calls for the same key; duplicates wait for the original and receive the same result.

package main

import (
	"fmt"

	"pkg.venceslau.dev/singleflight"
)

func main() {
	var g singleflight.Group[string, string]

	v, err, _ := g.Do("key", func() (string, error) {
		return "value", nil
	})

	fmt.Println(v, err)
	// Output: value <nil>
}

DoChan

Like Do, but returns a channel that receives a typed Result[V] when ready. Results are shared across calls made with a duplicate key.

var g singleflight.Group[string, string]

block := make(chan struct{})
res1c := g.DoChan("key", func() (string, error) {
	<-block
	return "func 1", nil
})
res2c := g.DoChan("key", func() (string, error) {
	<-block
	return "func 2", nil
})
close(block)

res1 := <-res1c
res2 := <-res2c

fmt.Println("Shared:", res2.Shared)          // Shared: true
fmt.Println("Equal results:", res1.Val == res2.Val) // Equal results: true
fmt.Println("Result:", res1.Val)             // Result: func 1

Forget

Drop the in-flight suppression entry for a key so the next call re-runs fn instead of joining the original.

g.Forget("key")

For runnable, tested examples see examples_test.go.

Updates & Versioning

• This package will be kept in sync with the original golang.org/x/sync/singleflight package until it adds native generic support.
• Version tags will align with the original package's versioning.
• If you notice an update before I do, please open an issue or submit a pull request.