add more guidelines to DEVELOPMENT.md

DEVELOPMENT.md

@@ -27,22 +27,26 @@ ref.read(MyController.provider.notifier).helperMethod()
 We use an object oriented style for controllers, where `provider` is a static member on the controller class. E.g.
 
 ```dart
-class MyController extends AsyncNotifier<DataThisControllerExposes> {
-  final SomeInputType input;
-  MyController(this.input);
-
+class MyController(final SomeInputType input)
+    extends AsyncNotifier<DataThisControllerExposes> {
   @override
   Future<DataThisControllerExposes> build() async {
     return input.foo;
   }
 
   static final provider =
-	AsyncNotifierProvider.family<MyController, DataThisControllerExposes, SomeInputType>(
-	  AuthorController.new,
-	);
+      AsyncNotifierProvider.family<MyController, DataThisControllerExposes, SomeInputType>(
+        MyController.new,
+      );
 }
 ```
 
+#### `watch` vs `read`
+
+Only use `ref.watch` in a `build` method, where you want to rebuild when the value changes. Everywhere else, like callbacks, `useEffect`, and methods on a controller, use `ref.read`.
+
+Use `.select` to narrow down what you depend on, e.g. `ref.watch(RoomsController.provider.select((rooms) => rooms[roomId]))`.
+
 Providers which are not controllers, e.g. they expose no data, only methods, should instead live in `lib/helpers/`. For an example, see `lib/helpers/launch_helper.dart`. Other, non-provider helpers, like extensions or helper methods can also go in `lib/helpers/`.
 
 ### Don't use StatefulWidgets ([Flutter Hooks](https://pub.dev/packages/flutter_hooks))
@@ -63,6 +67,34 @@ When possible, we prefer not to create global variables or methods. You can usua
 
 I'm also not a big fan of private methods or variables, but this is contextual.
 
+### Modern Dart syntax
+
+We try to use newer Dart language features where they make code shorter:
+
+- Primary constructors for classes, including widgets, e.g. `class const MemberList(final String roomId, {super.key}) extends HookConsumerWidget`.
+- Dot shorthands wherever the type can be inferred, e.g. `.new(...)`, `padding: .all(8)`, `relationType == .reply`.
+- Patterns and switch expressions over null checks and casts, e.g. `if (event.content case MessageContent(:final body?))` rather than checking `is` then using `!`.
+
+### Prefer `map` over inline `for` loops
+
+When building a list (or set, or map) from another collection, use `.map`, `.expand` and friends rather than a `for` inside the collection literal:
+
+```dart
+// Prefer
+children: rooms.map((room) => RoomTile(room)).toList(),
+
+// Over
+children: [for (final room in rooms) RoomTile(room)],
+```
+
+Regular `for` statements are fine for logic that doesn't just build a collection.
+
+### Async values and errors
+
+When rendering an `AsyncValue`, use the `betterWhen` extension, which shows our standard loading and error widgets, or a switch expression if you need more control (e.g. `AsyncData(:final value) || AsyncLoading(:final value?)` to keep showing old data while reloading).
+
+For futures started from the UI that nothing awaits, like button presses, add `.onError(showError)` so failures are shown to the user instead of being lost.
+
 ## LLM/AI Assisted Contributions
 
 LLM generated code is NOT allowed. All contributions should be written by humans. Using LLMs for interacting with others, e.g. for Comments, PRs, etc, is also not allowed.