added FindFirstIndex and FindLastIndex

filter.go

@@ -19,12 +19,20 @@ func FindFirst[T any](slice []T, f func(T) bool) (T, bool) {
 	return *new(T), false
 }
 
-func FindLast[T any](slice []T, f func(T) bool) (T, bool) {
+func FindFirstIndex[T any](slice []T, f func(T) bool) (int, bool) {
-	for i := len(slice); i >= 0; i-- {
+	for i, v := range slice {
-		v := slice[i]
 		if f(v) {
-			return v, true
+			return i, true
 		}
 	}
-	return *new(T), false
+	return -1, false
+}
+
+func FindLastIndex[T any](slice []T, f func(T) bool) (int, bool) {
+	for i := len(slice); i >= 0; i-- {
+		if f(slice[i]) {
+			return i, true
+		}
+	}
+	return -1, false
 }