Make WithWorkers support slices and maps with generic key-value pairs

main.go

@@ -12,34 +12,47 @@ import (
 	"golang.org/x/time/rate"
 )
 
-func WithWorkers[T any](workers int, arr []T, fn func(worker int, item T)) {
-	workersChan := make(chan struct{}, workers)
-	ingestChan := make(chan T, len(arr))
-
-	for _, item := range arr {
-		ingestChan <- item
+func WithWorkers[K comparable, V any, C []V | map[K]V](
+	workers int,
+	items C,
+	fn func(worker int, key K, value V),
+) {
+	type KV struct {
+		// A bit of type weaving...
+		Key   any
+		Value V
 	}
-	close(ingestChan)
 
-	wg := sync.WaitGroup{}
+	n := len(items)
+	ingestChan := make(chan KV, n)
+
+	go func() {
+		switch v := any(items).(type) {
+		case []V:
+			for i, it := range v {
+				ingestChan <- KV{Key: i, Value: it}
+			}
+		case map[K]V:
+			for key, it := range v {
+				ingestChan <- KV{Key: key, Value: it}
+			}
+		}
+		close(ingestChan)
+	}()
+
+	var wg sync.WaitGroup
+	wg.Add(workers)
 	for i := 0; i < workers; i++ {
-		workersChan <- struct{}{}
-		wg.Add(1)
 		go func(worker int) {
 			defer wg.Done()
-			defer func() { <-workersChan }()
-			for {
-				item, ok := <-ingestChan
-				// We're done processing totally
-				if !ok {
-					return
-				}
-				fn(worker, item)
+			for v := range ingestChan {
+				fn(worker, v.Key.(K), v.Value)
 			}
 		}(i)
 	}
 	wg.Wait()
 }
+
 func Batched[T any](arr []T, batchSize int, fn func(batch []T)) {
 	for i := 0; i < len(arr); i += batchSize {
 		start := i