Skip to main content

Dart 1.21: Generic Method Syntax

Dart 1.21 is now available. It introduces support for generic method syntax along with a few popular convenience features. Get it now!

Generic method syntax




Until now, Dart's generic support was limited to classes, such as List<T>. Dart 1.21 introduces syntax allowing type arguments on methods and functions.

   T first<T>(List<T> ts) {
     return ts.length == 0 ? throw new ArgumentError('Empty list!') : ts[0];
   }

Note the return type, T. This enables call sites to preserve type information from arguments. Try to write the same function without a type argument, and you'll see that the return type must be Object – there is no other way we can make it work on all lists. For more examples, check out the Using Generic Methods article. For even more details, the informal specification is the place to go.

We've had generic methods and functions for a while in strong mode. 1.21 introduces support for generic method syntax even without strong mode. Libraries can use this feature and work in both contexts, providing a stepping stone to full generic methods in all Dart code.

However, this feature does not yet provide full runtime support for generic methods outside DDC. In particular, type arguments are not reified (i.e., they have no representation at runtime). Libraries must avoid constructs where the runtime value of type arguments matters, in order to work in both modes. For example, x is T will not work outside strong mode if T is a method type argument. The analyzer marks such cases as errors, so you'll have tool support to avoid them. (Note: If you are using IntelliJ, support is available in WebStorm 2016.3.2 RC / IntelliJ IDEA 2016.3.1 RC, and later.)

Convenience features


1.21 also introduces a couple of much requested convenience features. You can now use = to specify a default value for a named argument.

   enableFlags({bool hidden: false}) { … }

can now be replaced by

   enableFlags({bool hidden = false}) { … }

We’re also introducing access to initializing formals, e.g., x is now in scope in the initializer list such that we can use it to initialize y in this example:

   class C { 
     var x, y; 
     C(this.x): y = x; 
   } 

As with any new language feature, it is critical for package authors to update pubspec.yaml with a latest SDK version.

   name: my_cool_dart_package
   environment:
     sdk: '>=1.21.0 <2.0.0'

This ensures users on older SDKs aren't broken when they update their packages.

For more details on these and other changes in 1.21, see the full changelog. Otherwise, download the latest release, and let us know what you think!

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 Рeven more so Рfrom 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 …