erts: Implement map iterator using a stack

This version does not work great as the subtrees
created are not proper hash maps. Also it is not
all that performant as the extra allocations to
keep the stack there is expensive.

1 files changed, 11 insertions, 2 deletions

diff --git a/lib/stdlib/src/maps.erl b/lib/stdlib/src/maps.erl
index 7ed32a3988..0da12cf8e2 100644
--- a/lib/stdlib/src/maps.erl
+++ b/lib/stdlib/src/maps.erl
@@ -32,7 +32,7 @@
          new/0, put/3, remove/2, take/2,
          to_list/1, update/3, values/1]).
 
--opaque iterator() :: [{term(), term()}].
+-opaque iterator() :: [{term(), term()}] | [[pos_integer() | map()]].
 
 -export_type([iterator/0]).
 
@@ -279,7 +279,10 @@ size(Val) ->
       Iterator :: iterator().
 
 iterator(Map) when is_map(Map) ->
-    maps:to_list(Map);
+    case maps:size(Map) < 42 of
+        true -> maps:to_list(Map);
+        false -> [[1 | Map]]
+    end;
 iterator(M) ->
     erlang:error(error_type(M),[M]).
 
@@ -289,6 +292,12 @@ iterator(M) ->
       V :: term(),
       NextIterator :: iterator().
 next([]) -> none;
+next([[Index | Map] | St]) ->
+    case erts_internal:map_get_index(Index, Map) of
+        SubMap when is_map(SubMap) -> next([[1 | SubMap], [Index+1|Map] | St]);
+        [K|V] -> {K,V,[[Index+1 | Map] | St]};
+        none -> next(St)
+    end;
 next([{K, V} | I]) ->
     {K, V, I}.