Merge pull request #938 from pguyot/w45/implement-map-foreach

Implement `maps:foreach/2`

libs/estdlib/src/maps.erl

@@ -50,6 +50,7 @@
     find/2,
     filter/2,
     fold/3,
+    foreach/2,
     map/2,
     merge/2,
     remove/2,
@@ -335,6 +336,33 @@ fold(_Fun, _Init, Map) when not is_map(Map) ->
 fold(_Fun, _Init, _Map) ->
     error(badarg).
 
+%%-----------------------------------------------------------------------------
+%% @param   Fun     function to call with every key-value pair
+%% @param   MapOrIterator the map or map iterator over which to iterate
+%% @returns `ok'
+%% @doc Iterate over the entries in a map.
+%%
+%% This function takes a function used to iterate over all entries in a map.
+%%
+%% This function raises a `badmap' error if `Map' is not a map or map iterator,
+%% and a `badarg' error if the input function is not a function.
+%% @end
+%%-----------------------------------------------------------------------------
+-spec foreach(
+    Fun :: fun((Key :: key(), Value :: value()) -> any()),
+    MapOrIterator :: map_or_iterator()
+) -> ok.
+foreach(Fun, Map) when is_function(Fun, 2) andalso is_map(Map) ->
+    iterate_foreach(Fun, maps:next(maps:iterator(Map)));
+foreach(Fun, [Pos | Map] = Iterator) when
+    is_function(Fun, 2) andalso is_integer(Pos) andalso is_map(Map)
+->
+    iterate_foreach(Fun, maps:next(Iterator));
+foreach(_Fun, Map) when not is_map(Map) ->
+    error({badmap, Map});
+foreach(_Fun, _Map) ->
+    error(badarg).
+
 %%-----------------------------------------------------------------------------
 %% @param   Fun     the function to apply to every entry in the map
 %% @param   Map     the map to which to apply the map function
@@ -463,6 +491,13 @@ iterate_fold(Fun, {Key, Value, Iterator}, Accum) ->
     NewAccum = Fun(Key, Value, Accum),
     iterate_fold(Fun, maps:next(Iterator), NewAccum).
 
+%% @private
+iterate_foreach(_Fun, none) ->
+    ok;
+iterate_foreach(Fun, {Key, Value, Iterator}) ->
+    _ = Fun(Key, Value),
+    iterate_foreach(Fun, maps:next(Iterator)).
+
 %% @private
 iterate_map(_Fun, none, Accum) ->
     Accum;

tests/libs/estdlib/test_maps.erl

@@ -37,6 +37,7 @@ test() ->
     ok = test_find(),
     ok = test_filter(),
     ok = test_fold(),
+    ok = test_foreach(),
     ok = test_map(),
     ok = test_merge(),
     ok = test_remove(),
@@ -143,6 +144,42 @@ test_fold() ->
     ?ASSERT_ERROR(maps:fold(not_a_function, any, maps:new()), badarg),
     ok.
 
+collect_foreach(Acc) ->
+    Self = self(),
+    receive
+        {Self, Key, Value} ->
+            collect_foreach([{Key, Value} | Acc])
+    after 0 -> Acc
+    end.
+
+test_foreach() ->
+    % maps:foreach/2 was introduced with OTP 24.
+    HasForeach =
+        case erlang:system_info(machine) of
+            "BEAM" -> erlang:function_exported(maps, foreach, 2);
+            "ATOM" -> true
+        end,
+    if
+        HasForeach ->
+            Self = self(),
+            Fun = fun(Key, Value) -> Self ! {self(), Key, Value} end,
+            ok = maps:foreach(Fun, maps:new()),
+            ?ASSERT_EQUALS(collect_foreach([]), []),
+            ok =
+                receive
+                    {Self, _, _} -> fail
+                after 0 -> ok
+                end,
+            ok = maps:foreach(Fun, #{a => 1, b => 2, c => 3}),
+            ?ASSERT_EQUALS(lists:sort(collect_foreach([])), [{a, 1}, {b, 2}, {c, 3}]),
+            ok = check_bad_map(fun() -> maps:foreach(Fun, id(not_a_map)) end),
+            ok = check_bad_map_or_badarg(fun() -> maps:foreach(not_a_function, id(not_a_map)) end),
+            ?ASSERT_ERROR(maps:foreach(not_a_function, maps:new()), badarg),
+            ok;
+        true ->
+            ok
+    end.
+
 test_map() ->
     Fun = fun(_Key, Value) -> 2 * Value end,
     ?ASSERT_EQUALS(maps:map(Fun, maps:new()), #{}),