Big turnoff with Dart is the lack of json (de) serialization -- kind of shocking to have to resort to source code generation libraries in a modern language.
Also, statement based instead of expression based, and not immutable by default are kind of a drag; not the end of the world but a bit unpleasant, IMO.
Also, statement based instead of expression based, and not immutable by default are kind of a drag; not the end of the world but a bit unpleasant, IMO.