Feature request: infer class from type annotation in new expression.

[DartBot]

This issue was originally filed by michaels...@gmail.com

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What steps will reproduce the problem?

class Point {
  Point(num this.x, num this.y);
  num x, y;
}

main() {
  Point p = new(3, 5);
  print(p.x + ', ' + p.y);
}

What is the expected output? What do you see instead?

In the line:

   Point p = new(3, 5);

The above should be interpreted as short-hand for:

   Point p = new Point(3, 5);

What version of the product are you using? On what operating system?

   Using try-dart-lang:
   http://try-dart-lang.appspot.com/s/3i8X

Please provide any additional information below.

[munificent]

Having to type Point twice is indeed tedious. How about just doing:

main() {
  var p = new Point(3, 5);
  print(p.x + ', ' + p.y);
}

[DartBot]

This comment was originally written by jat@google.com

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@2 - the difference is p is of type Dynamic, not Point.

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Removed Type-Defect label.
Added Type-Enhancement, Area-Language, Triaged labels.

[DartBot]

This comment was originally written by michaels...@gmail.com

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@1, to echo jat's comment, it would seem that your suggestion makes 'p' have declared-type dynamic with Point as the runtime type, while the syntax I was suggesting would have both a declared and runtime type of Point.

Also, an enhancement beyond even this, would be to do something like:

   Map<K, V> m = new();

Where Map is an interface, and some particular implementing class is declared to be the "default" implementation for that interface, which would not work with the other syntax.

[gbracha]

Type annotations do not change the behavior of the program. This is a crucial design principle of Dart. If we start changing what code does based on types, the entire type discipline will become unmanageable. Of course, the proposal only works in certain scenarios, as new expressions can appear in many contexts. What happens when the annotation is an abstract class or an interface without a factory? As the number of special rules and cases multiply, languages collapse under the weight of unforeseen interaction.

 I also find this unreadable. Newcomers in particular will end up baffled by an endless set of shorthands that they need to learn. Program readabilty is more important than the effort involved in typing.

Reducing the need to type will likely be achieved via tool support that will add type annotations for you. Conceivably, name completion in the IDE could do what you're asking for as well. The language will not.

I'm renaming the bug to make clear what it is actually about.

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Added WontFix label.
Changed the title to: "Feature request: infer class from type annotation in new expression.".