Support shorthand class creation syntax

[agrosner]

For classes with a single constructor that takes in a few values.

class User {
  final String firstName;
  final String lastName;

  User({@required this.firstName, @required this.lastName});
}

It would be much cleaner and concise to simply allow a "primary constructor":

class User({@required this.firstName, @required this.lastName}) {
  final String firstName;
  final String lastName;
}

Duplicating constructor and class declaration seems a little clunky. When we have more fields,
this duplication is further known and wish we could take it a step further to allow:

class User({@required final String firstName, @required final String lastName});

Less duplication in code will lead to nice details in our widgets for flutter like from this:

class AppDetails extends StatefulWidget {
  final String url;
  final String jobName;

  AppDetails({@required this.url, @required this.jobName});

  @override
  AppDetailsState createState()  => new AppDetailsState(this.url, initialJobName: jobName);
}

class AppDetailsState extends State<AppDetails> {
  String selectedJobName;
  final String jobUrl;

  AppDetailsState(this.jobUrl, {@required String initialJobName}) {
    this.selectedJobName = initialJobName;
  }

  // state implementation below

}

to this:

class AppDetails({@required final String url, @required final String jobName})
 extends StatefulWidget {
  @override
  AppDetailsState createState() => new AppDetailsState(this.url, initialJobName: jobName);
}

class AppDetailsState(final String jobUrl, {@required String initialJobName}) 
 extends State<AppDetails> {

  // state implementation below

from 17 lines of boilerplate to 8.

[leafpetersen]

cc @munificent @lrhn

[lrhn]

I'm unable to find other requests for the same thing (which surprises me, except that I can never find anything using GitHub search).

What we are asking for here is a shorter syntax to write a simple class, without having to repeat the field names (or even class name) in a constructor.

[zoechi]

@lrhn perhaps dart-lang/sdk#10551, dart-lang/sdk#10374

[SAGARSURI]

Is there something similar to inline classes in Dart?

[eernstg]

No, we don't have that currently. The main property of an inline class (corresponding to Haskell newtype) is that it is a zero cost wrapper, in the sense that it is a new type which is distinct from (and not assignable to) the type of the wrapped value, but the run-time representation is just that wrapped value. One example of work in this direction is https://github.com/dart-lang/language/blob/master/working/static%20wrapper%20types/feature-specification.md.

[SAGARSURI]

Thanks @eernstg for the info. Excited for the above feature to be added in Dart.

[eernstg]

Moving this issue to the language repo, it would be a language mechanism.

[kevmoo]

Seee #698 – covers your case nicely I think!

[leafpetersen]

We're tracking this here, closing in favor of that issue (let me know if I've missed something distinct about this request.