added default unmapper functions for OfMap

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
 }

of.go

@@ -14,3 +14,15 @@ func OfMap[K comparable, V, T any](m map[K]V, unmapper func(K, V) T) []T {
 	}
 	return out
 }
+
+// UnmapKey is an unmapper function which returns the map key only
+// and discards its value. It is supposed to be used with OfMap
+func UnmapKey[K comparable, V any](key K, _ V) K {
+	return key
+}
+
+// UnmapValue is an unmapper function which returns the map value only
+// and discards its key. It is supposed to be used with OfMap
+func UnmapValue[K comparable, V any](_ K, value V) V {
+	return value
+}