refactor: Only loop once on "cached_properties" when building slotted classes (#1290)

Only loop once on "cached_properties" when building slotted classes

Previously the cached_properties dict was read three times.

Co-authored-by: Hynek Schlawack <hs@ox.cx>

src/attr/_make.py

@@ -931,19 +931,13 @@ class _ClassBuilder:
         # To know to update them.
         additional_closure_functions_to_update = []
         if cached_properties:
-            # Add cached properties to names for slotting.
-            names += tuple(cached_properties.keys())
-
-            for name in cached_properties:
-                # Clear out function from class to avoid clashing.
-                del cd[name]
-
-            additional_closure_functions_to_update.extend(
-                cached_properties.values()
-            )
-
             class_annotations = _get_annotations(self._cls)
             for name, func in cached_properties.items():
+                # Add cached properties to names for slotting.
+                names += (name,)
+                # Clear out function from class to avoid clashing.
+                del cd[name]
+                additional_closure_functions_to_update.append(func)
                 annotation = inspect.signature(func).return_annotation
                 if annotation is not inspect.Parameter.empty:
                     class_annotations[name] = annotation