fn: add concurrent map operation for slices

fn/slice.go

@@ -1,5 +1,7 @@
 package fn
 
+import "sync"
+
 // All returns true when the supplied predicate evaluates to true for all of
 // the values in the slice.
 func All[A any](pred func(A) bool, s []A) bool {
@@ -168,3 +170,21 @@ func ZipWith[A, B, C any](f func(A, B) C, a []A, b []B) []C {
 
  return res
 }
+
+// ForEachConc maps the argument function over the slice, spawning a new
+// goroutine for each element in the slice and then awaits all results before
+// returning them.
+func ForEachConc[A, B any](f func(A) B, as []A) []B {
+ wait := sync.WaitGroup{}
+ bs := make([]B, len(as))
+ for i, a := range as {
+ i, a := i, a
+ wait.Add(1)
+ go func() {
+ bs[i] = f(a)
+ wait.Done()
+ }()
+ }
+ wait.Wait()
+ return bs
+}