feat: change slice.Reduce return type

slice.go

@@ -134,10 +134,12 @@ func Map[T any, R any, F MapFunc[T, R]](ss []T, funcInterface F) []R {
 	return result
 }
 
-type AccumulatorFunc[T any] func(acc T, i int, s T) T
+type AccumulatorFunc[T any, R any] interface {
+	~func(acc R, i int, s T) R
+}
 
 // Reduce (aka inject) iterates over the slice of items and calls the accumulator function for each pass, storing the state in the acc variable through each pass.
-func Reduce[T any](items []T, initialAccumulator T, f AccumulatorFunc[T]) T {
+func Reduce[T any, R any, F AccumulatorFunc[T, R]](items []T, initialAccumulator R, f F) R {
 	if items == nil {
 		return initialAccumulator
 	}

slice_test.go

@@ -56,6 +56,24 @@ func TestReduce(t *testing.T) {
 	})
 
 	require.Equal(t, "55", result)
+
+	type OddEven struct {
+		Odd  int
+		Even int
+	}
+
+	s2 := []int{0, 1, 2, 3, 4}
+
+	result2 := slice.Reduce(s2, OddEven{}, func(acc OddEven, i int, s int) OddEven {
+		if s%2 == 0 {
+			acc.Even++
+		} else {
+			acc.Odd++
+		}
+		return acc
+	})
+
+	require.Equal(t, OddEven{Odd: 2, Even: 3}, result2)
 }
 
 func TestSelect(t *testing.T) {