added default unmapper functions for OfMap

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
+}