Monday, August 31, 2015

Dart 1.12 Released, with Null-Aware Operators and more

Dart 1.12.0 is now released! It contains the new null-aware operators language feature, and enhancements to pub, Observatory, dartdoc, and much more.

Null-aware operators

The new null-aware operators help you reduce the amount of code required to work with references that are potentially null. This feature is a collection of syntactic sugar for traversing (potentially null) object calls, conditionally setting a variable, and evaluating two (potentially null) expressions.

Click or tap the red Run button below to see them in action.

??

  if null operator. `expr1 ?? expr2` evaluates to `expr1` if not `null`, otherwise `expr2`.


??=

  null-aware assignment. `v ??= expr` causes `v` to be assigned `expr` only if `v` is `null`.


x?.p

  null-aware access. `x?.p` evaluates to `x.p` if `x` is not `null`, otherwise evaluates to `null`.


x?.m()
  
  null-aware method invocation. `x?.m()` invokes `m` only if `x` is not `null`.


Learn more about Dart's null-aware operators in our Language Tour.

.packages file

We continue in our efforts to eliminate symlinks by introducing the .packages file, which is a new way to specify where to find package dependencies. The pub package manager now writes a .packages file when getting or upgrading dependencies, and the VM and dartanalyzer use the .packages file for package resolution.

The Dart SDK still generates symlinks in 1.12, but the .packages file gets us closer to eliminating them. If you have tools that introspect packages, now is a good time to investigate the .packages file.

dartdoc

The dartdoc tool is a new way to generate beautiful, fast-loading API docs. It replaces dartdocgen, which we plan to remove from the SDK as soon as 1.13. dartdoc generates static docs, helps you search with find-as-you-type, and looks great on a mobile device.

dartfmt

Speed up your code reviews by automatically formatting your code. The dartfmt tool has been largely rewritten to support better handling for long argument lists, smarter indentation for cascades, nested functions, and collections, and fixes over 50 issues.

Observatory

Help identify memory leaks with Observatory's updated allocation profiler. Turn it on for a class, and track where instances of that class are created. Also new in 1.12 is support for dart:developer's log() function, which your app can use to stream log calls into Observatory's (or any connected debugger) console.

Stepping through async/await code has been significantly improved with Observatory's new anext command. You can now step over an await call, onto the next line of your code.

pub

The pub run commands can now toggle checked mode, with --checked. Pub now writes a .packages file when getting, upgrading, and globally activating your packages.

Lots more

The Dart SDK 1.12 CHANGELOG has lots more details about various API tweaks. We look forward to your feedback

Thursday, August 20, 2015

A New Way to Share with DartPad

Back in May, we announced the release of DartPad 1.0, a clean and zero-install tool that helps you explore Dart. To create a seamless learning experience for both experienced and new developers, today we released embeddable pads! You can now add live Dart code to web pages.

Embeddable pads have the full power of the standalone DartPad:

Tutorials and guides can use embeddings to quickly demonstrate concepts on the fly:

You can also open embedded pads in DartPad to further edit and share code. For more information, view the embedding guide.

Head over to dartpad.dartlang.org and share your first pad! We hope you enjoy this new addition and provide us with feedback—remember, sharing is caring!

Posted by George He, Chief Sharing Operator

Tuesday, August 11, 2015

5% smaller output from dart2js

dart2js now produces up to 5% smaller output in the latest dev channel release of the Dart SDK.
We measured a 5% reduction on the minified and zipped dart2js output for one of the larger Dart-based apps in Google with source code size around 17MB. While we’ve seen a 5% reduction on a large app, your milage may vary and improvements are expected to increase with the size of your app. This improvement comes on top of a previous 3% reduction since the beginning of this year.
The idea behind the latest improvement is quite simple: The symbols that will occur most often in the generated output should be assigned the shortest minified names. So when minifying the code, we rename according to the frequency of each symbol in such a way that a high frequency results in a short name in the output.

This new frequency-based namer generally produces smaller output, which is great for deployment. It does however also result in different name allocations and thus “diffing” before/after the change will not produce useful outcomes. Furthermore, with the new scheme a small change in the Dart program might lead to major changes in the naming in the output. If output stability is more important than output size, you can still use the old namer. Simply use the option --no-frequency-based-minification when invoking dart2js.

We are making the new improved namer available on dev channel to get early feedback from you in time before the first release of 1.12 on the stable channel expected later this summer. Please give it a try and report any bugs you might find.

Posted by Stephan Herhut, Frequency-Based Minifier