Monday, July 15, 2013

Notes from the July 8 Dart language design meeting

The incomporable Bob Nystrom fills us in on the language design discussions taking place amongst Dart engineers. Here are his notes from the July 8th language meeting:

Here's my notes!

JS interop and proxies

Lars tried to make a little app using JS interop. He gets warnings from dart2js because JS interop returns a proxy. The only way to get rid of the warnings is to edit the interop package itself to make it return the dynamic type.

Gilad says we don't currently have a solution for general purpose proxies, though we've discussed a couple.

The biggest problem is checked mode. If it was just static warnings, we could do an annotation or something to turn off the warning. For general purpose proxies, "implements dynamic" may be the best thing: it is a black hole that implements anything.

We will have to educate people: most of the time you want to implement some specific type and not turn them all off like this.

One thing Lars noticed when playing with JS interop: using it from the Editor doesn't report anything, but if you invoke dart2js from the command-line, warnings come out.

The type checker in the analyzer in the Editor doesn't report problems here.

Brian says earlier they had gotten lots of complaints about warnings from code that implements noSuchMethod so they put code in there to hide those warnings. They were going to tear that out to follow the spec, but heard something may be coming in spec for this, so they haven't taken it out yet. Basically, if you implement noSuchMethod, all sorts of warnings are blocked.

Gilad will send some spec language.

Unused arguments to closures and truthiness

The Angular people sent a doc suggesting some language improvements. Based on that, Kasper wrote proposal where you can invoke a closure with too many arguments. Another idea is some sort of special apply method. The question is if it's sufficient for the angular folks.

Gilad thinks a special apply is a good idea.

They also requested some sort of operator for truthiness. It isn't very composable in Lars' mind. They will discuss it with them in September when they are all in Denmark.

Cheers!


As always, view the changelog for the full list of changes, and to get started with the Editor see our tutorial.

Thursday, July 11, 2013

Introducing polymer.dart

Dart engineer John Messerly announces the launch of polymer.dart, a port of the Polymer stack. The Web UI package will be maintained for some time, but will eventually be replaced by polymer.dart.

Here is John's original post introducing polymer.dart:

Hello Dartisans,

Since we started Web UI, we've had a goal to bring the latest web standards like Web Components and Model-Driven Views to Dart developers. There have been some great developments since we started:

  • Web Components has progressed into a set of detailed specs (Custom Elements, Shadow DOM, HTML Templates, HTML Imports) with interest and implementation by multiple browser vendors.
  • Model-Driven Views has new APIs (Node.bind, TemplateElement.model) that allow custom elements to participate in the binding system, as well as the ability to plug in custom syntax, such as the fancy_syntax package.
  • dart:mirrors is now implemented in dart2js!
  • Last but not least: the development of the Polymer project. Polymer is a new type of JavaScript library for the web that builds on top of these emerging standards.

Today we continue our mission by publishing the beginnings of polymer.dart, our port of the Polymer stack. We’re pushing several packages to Pub: observe, mdv, shadow_dom, and the polymer.dart package.  The Dart team is collaborating with the Polymer team to ensure that polymer.dart elements and polyfills are fully compatible with Polymer.

This is only the beginning. Polymer and web components are evolving, and we’re going to keep bringing that to you. Some of the things we’ll be working on are:
  • declarative <polymer-element> and custom elements.
  • more new, up-to-date polyfill packages, like html_imports.
  • removing the mandatory compiler step for polymer.dart. Just edit, save & refresh!
  • bring the Polymer UI elements to Dart.
  • up to date documentation for all of this shiny new stuff.

It's still very early for polymer.dart, but we welcome you to try out the new packages. We’ll be maintaining the web_ui package for a considerable time, but will eventually be sunsetting it in favor of Polymer. Thanks in advance for your feedback as we continue the port and evolve the specs and implementations. We hope you’re as excited as we are about Polymer, and can't wait to see what you build!

Thanks!