Add assert that callback to write is not async

packages/realm_dart/lib/src/realm_class.dart

@@ -346,11 +346,14 @@ class Realm implements Finalizable {
  /// Checks whether the `Realm` is in write transaction.
  bool get isInTransaction => realmCore.getIsWritable(this);
 
+ bool _isSubtype<S, T>() => <S>[] is List<T>;
+
  /// Synchronously calls the provided callback inside a write transaction.
  ///
  /// If no exception is thrown from within the callback, the transaction will be committed.
  /// It is more efficient to update several properties or even create multiple objects in a single write transaction.
  T write<T>(T Function() writeCallback) {
+ assert(!_isSubtype<T, Future>(), 'writeAsync should be used for async operations');
  final transaction = beginWrite();
 
  try {

packages/realm_dart/test/realm_test.dart

@@ -1269,6 +1269,11 @@ void main() {
  expect(realm.all<Person>().length, 0); // everything is rolled back
  });
 
+ test('Realm.write with async callback', () {
+ final realm = getRealm(Configuration.local([Person.schema]));
+ expect(() => realm.write(() async {}), throwsA(isA<AssertionError>()));
+ });
+
  test('Transaction.commitAsync with a canceled token throws', () async {
  final realm = getRealm(Configuration.local([Person.schema]));