Optimize sets:is_empty/1

Author: juhlig

lib/stdlib/src/sets.erl

@@ -311,7 +311,7 @@ false
 -doc(#{since => <<"OTP 21.0">>}).
 -spec is_empty(Set) -> boolean() when
       Set :: set().
-is_empty(#{}=S) -> map_size(S) =:= 0;
+is_empty(#{}=S) -> S =:= #{};
 is_empty(#set{size=Size}) -> Size =:= 0.
 
 -doc """
@@ -561,15 +561,17 @@ elements that are present in both sets.
       Set2 :: set(Element),
       Set3 :: set(Element).
 intersection(#{}=S1, #{}=S2) ->
-    case map_size(S1) < map_size(S2) of
+    Size1 = map_size(S1),
+    Size2 = map_size(S2),
+    case Size1 < Size2 of
         true ->
             Next = maps:next(maps:iterator(S1)),
             intersection_heuristic(Next, [], [],
-                                   floor(map_size(S1) * 0.75), S1, S2);
+                                   floor(Size1 * 0.75), S1, S2);
         false ->
             Next = maps:next(maps:iterator(S2)),
             intersection_heuristic(Next, [], [],
-                                   floor(map_size(S2) * 0.75), S2, S1)
+                                   floor(Size2 * 0.75), S2, S1)
     end;
 intersection(S1, S2) ->
     case size(S1) < size(S2) of