Select anything

CHANGELOG.md

@@ -5,6 +5,7 @@
 - The `gleam/erlang/process` module's `selecting_subjectless_record` function
   has been replaced by the `selecting_record2`, `selecting_record3`, and
   `selecting_record4` functions.
+- The `gleam/erlang/process` module gains the `select_anything` function.
 
 ## v0.14.0 - 2022-08-01
 

src/gleam/erlang/process.gleam

@@ -321,6 +321,24 @@ pub fn selecting_record4(
   insert_selector_handler(selector, #(tag, 4), handler)
 }
 
+type AnythingSelectorTag {
+  Anything
+}
+
+/// Add a catch-all handler to a selector that will be used when no other
+/// handler in a selector is suitable for a given message.
+///
+/// This may be useful for when you want to ensure that any message in the inbox
+/// is handled, or when you need to handle messages from other BEAM languages
+/// which do not use subjects or record format messages.
+///
+pub fn selecting_anything(
+  selector: Selector(payload),
+  mapping handler: fn(Dynamic) -> payload,
+) -> Selector(payload) {
+  insert_selector_handler(selector, Anything, handler)
+}
+
 external fn insert_selector_handler(
   Selector(payload),
   for: tag,

src/gleam_erlang_ffi.erl

@@ -168,6 +168,7 @@ select(Selector) ->
     Message.
 
 select({selector, Handlers}, Timeout) ->
+    AnythingHandler = maps:get(anything, Handlers, undefined),
     receive
         % Monitored process down messages.
         % This is special cased so we can selectively receive based on the
@@ -178,7 +179,10 @@ select({selector, Handlers}, Timeout) ->
 
         Msg when is_map_key({element(1, Msg), tuple_size(Msg)}, Handlers) ->
             Fn = maps:get({element(1, Msg), tuple_size(Msg)}, Handlers),
-            {ok, Fn(Msg)}
+            {ok, Fn(Msg)};
+
+        Msg when AnythingHandler =/= undefined ->
+            {ok, AnythingHandler(Msg)}
     after Timeout ->
         {error, nil}
     end.

test/gleam/erlang/process_test.gleam

@@ -285,6 +285,22 @@ pub fn selecting_record_test() {
     |> process.select(0)
 }
 
+pub fn selecting_anything_test() {
+  process.flush_messages()
+  send(process.self(), 1)
+  send(process.self(), 2.0)
+
+  let selector =
+    process.new_selector()
+    |> process.selecting_anything(dynamic.int)
+
+  assert Ok(Ok(1)) = process.select(selector, 0)
+  assert Ok(Error([
+    dynamic.DecodeError(expected: "Int", found: "Float", path: []),
+  ])) = process.select(selector, 0)
+  assert Error(Nil) = process.select(selector, 0)
+}
+
 pub fn linking_self_test() {
   assert True = process.link(process.self())
 }