Thursday, October 11, 2012

Notes from October 8 language design meeting

Dart engineer Bob Nystrom has posted the notes from the October 8 language design meeting. He writes:


Making throw an expression

Lars wondered what the motivation behind adding to the spec was. My recollection was that it was so you could use it in lambda-body methods:

  class ImmutableList implements List {
    void add(item) => throw new NotSupportedException();
  }

Kasper looked at the code to parse throw as an expression and found out it's hideous because of rethrows.

Lars wants to know more about the impact of this. How tightly does it bind when embedded in an expression? Do we want to allow it in a ternary operator? He wants to know more about the original motivation behind this.

Mixins

Lars suggested we could do the general purpose solution and allow constructors but he would prefer something stepwise where we don't allow constructors at first. You could still have fields but they would need initializers at the declaration. We can get some experience with the feature and this will probably solve more use cases.

Gilad is all for it and asked about the timeline.

I asked if we'd be able to make changes to corelib to take advantage of mixins once they are supported even if those happen to be breaking changes. The answer is yes, but we of course want to minimize breakage.

Library tags

I asked about the intent behind library tags. I thought you only needed them if you use part, but the spec says the only place you can omit them is scripts which have a main() method.

Kasper says we want to encourage people to name their libraries because you get nice benefits like it can tell you if you accidentally import the same library from two different paths, which would be confusing because you'll get two copies of your statics.

Right now, the spec is maybe stricter than our original intent, but its easier to loosen it over time than go the other way, so lets leave it as it is.

Cheers!