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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 strong mode – 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 of strong mode, and the large number of users already using it, we have decided to make strong mode the standard type system for Dart. This means that we will initiate a move to 2.0 in three phases: 1) strong mode is opt in, 2) strong mode is the default, and 3) strong mode is the only mode. We are making sure that Dart users have a smooth transition to the new type system, as explained in more detail below.

Moving to strong mode also enables the use of the new Dart development compiler (dartdevc, also known as DDC) instead of Dartium for web app development. With dartdevc you get faster developer cycles and can use any recent version of Chrome – unlocking among other things the use of bleeding edge browser features. Once the developer experience with dartdevc matches that of Dartium, we’ll stop maintaining Dartium.

You should continue to use dart2js to compile your final app. Where dartdevc is optimized for fast refreshes and easy debugging, dart2js is optimized for small generated code size and fast runtime of web apps.

As mentioned above, to help prepare for the transition to strong mode, we’re moving to 2.0 in three phases: In the current phase (phase 1) you can opt in to strong mode and dartdevc. Phase 2 will make strong mode the default, but you'll be able to opt out. Finally, phase 3 will make strong mode the only type system for Dart, and eventually we’ll remove Dartium.


We believe these changes will help you and your team be more productive when writing Dart apps. If you’d like to try out strong mode and dartdevc with your web apps, check out the Dart 1.24 announcement and follow the instructions in the Tool Changes section of the changelog. To use strong mode when building for mobile, check out flutter.io.

As always, we’d love to hear about your experiences with Dart and strong mode – especially if you encounter issues when transitioning to dartdevc and our new type system.

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Posted by Seth Ladd

(This is an "oldie but a goodie" misc@dartlang.org post originally written by Bob Nystrom. It is being posted here as the explanations still ring true.)

Bob writes:


"static", "final", and "const" mean entirely distinct things in Dart:

"static" means a member is available on the class itself instead of on instances of the class. That's all it means, and it isn't used for anything else. static modifies *members*.

"final" means single-assignment: a final variable or field *must* have an initializer. Once assigned a value, a final variable's value cannot be changed. final modifies *variables*.

"const" has a meaning that's a bit more complex and subtle in Dart. const modifies *values*. You can use it when creating collections, like const [1, 2, 3], and when constructing objects (instead of new) like const Point(2, 3). Here, const means that the object's entire deep state can be determ…