Skip to main content

Dec 10 Language Design Meeting Notes

Dart engineer Bob Nystrom has posted the notes from the December 10th language design meeting. He writes:

Mixins

We're down to arguing about syntax. Lars says, OK, here it is:

    class C extends S with M1, M2 { ... }

Mixins are linearized from right to left. This makes sense since the class body appears last but takes precedence, so we work backwards from that. Gilad has an updated proposal that he'll send out.

There is one corner case. If you want to mixin, you have to have an explicit superclass:

    class C extends Object with M1 { ... }

[Bob: This means that I believe we have the semantics and syntax for mixins nailed down now. Woo!]

throw as expression

They're looking to implement this in dart2js now. Even with the restriction on rethrows, it still feels tricky. Since throw takes an arbitrary expression on the right, including a conditional one, there are some corner cases related to how it binds.

Lars: Is rethrow an expression?
Gilad: It is in the spec, but the implementations don't support it.
Kasper: It is hard to parse. We have to lookahead to tell if we're at the beginning of an expression.
Lars: Let's make both kinds of throws an expression and rename rethrow to use a "rethrow" contextual keyword. It's a rarely used feature. Better?
Gilad: I'll talk to the implementors and work through something.

Metadata in corelib

Brian: There is a faction that says certain metadata constructs need to be in the language spec before they can be put into the core library. Are all tools required to have certain behavior because certain metadata is in the core library? For example, does dart2js have to emit some kind of notification if you use @deprecated?

Gilad: If we want metadata that does something magical then it should be in the spec. If it's just in tools, we shouldn't.

[Bob: I think an example of an annotation with magic behavior is one that says "don't tree-shake this".]

Kasper: If we use them in our libraries, we have to tell people what they mean. So it has to be specified somewhere, even if informally.

Gilad: Sure, but that applies to the library API itself too. You have to document it.

Lars: I would like to minimize the use of annotations in core library. We don't want using them to be part of normal style. Java uses them everywhere.

Configuration-specific code

Lars suggests we could have annotation to put on constants that lets you override its value from the outside from something like a command line argument.

We'll discuss this more after M2.

Cheers!

As always, we invite you to join our Dart mailing list, ask questions on Stack Overflow, or file feature requests on dartbug.com.

Popular posts from this blog

A stronger Dart for everyone

We are constantly asking ourselves:
How do we make developers even more productive when writing Dart apps? We believe that a critical part of the answer to this question is to make strongmode – a sound static type system for Dart – the standard for all Dart developers.

Teams that use Dart to build apps like Soundtrap, AdWords, AdSense, and Greentea say they really enjoy using strong mode features, such as early error detection. In fact, teams that have switched completely to strong mode cite not only early error detection but also better code readability and maintainability as major benefits. We hear this both from small teams and – even more so – from large teams with hundreds of developers writing and maintaining millions of lines of Dart code. As Björn Sperber from Soundtrap says,
Strong mode and the smooth integration with IntelliJ is a joy to use and a huge improvement. If you’ve tried out Flutter, you’ve already used strong mode checks from the Dart analyzer.

Given the benefits …

AngularDart 3.0: Easy upgrade, better performance

AngularDart 3.0 is now available. It brings better performance and smaller generated code, while also making you more productive.


Version 3.0 is an evolution: although it has some breaking changes (detailed below), it is a smooth upgrade due to minimal public API adjustments. Most of the progress is under the hood—in code quality, stability, generated code size, performance, and developer experience.

Code quality:
2731 instances of making the framework code more type safe (using sound Dart).The AngularDart framework code size is down by 12%.Many additional style updates to the codebase:Changed to use idiomatic <T> for generic methods.Removed NgZoneImpl, all the code exists in NgZone now.Stability:
Many CSS encapsulation fixes due to update with csslib package.Fixed bugs with IE11.

Performance:
For the Mail sample app, we see 30% faster time-to-interactive (currently 3812 ms on a simulated 3G connection, measured via Lighthouse).Our large app benchmark shows 2x faster render times of…

Dart 1.24: Faster edit-refresh cycle on the web & new function type syntax

Dart 1.24 is now available. It includes the Dart Development Compiler and supports a new generic function type syntax. Get it now!


Figure 1: DDC debugging in Chrome.

Some notable changes in this release:
pub serve now has support for the Dart Development Compiler. Unlike dart2js, this new compiler is modular, which allows pub to do incremental re-builds for pub serve.In practice what that means is you can edit your Dart files, refresh in Chrome (or other supported browsers), and see your edits almost immediately. This is because pub is only recompiling your package, not all packages that you depend on.There is one caveat with the new compiler, which is that your package and your dependencies must all be strong mode clean.You can also use the new compiler to run your tests in Chrome much more quickly than you can with dart2js.Read more in the changelog.You can now publish packages that depend on the Flutter SDK to pub. Moreover, pub.dartlang.org has started tagging Flutter plugins with …