Optimize lists:flatmap/2 for filtering

erlang · Aug 27, 2024 · 29bb2b4 · 29bb2b4
1 parent 1afaa45
commit 29bb2b4
Showing 1 changed file with 6 additions and 1 deletion.
diff --git a/lib/stdlib/src/lists.erl b/lib/stdlib/src/lists.erl
@@ -2113,7 +2113,12 @@ flatmap(F, List) when is_function(F, 1) ->
     flatmap_1(F, List).
 
 flatmap_1(F, [Hd | Tail]) ->
-    F(Hd) ++ flatmap_1(F, Tail);
+    case F(Hd) of
+        %% The two first clauses are an optimization.
+        [] -> flatmap_1(F, Tail);
+        [Elem] -> [Elem | flatmap_1(F, Tail)];
+        List -> List ++ flatmap_1(F, Tail)
+    end;
 flatmap_1(_F, []) ->
     [].