How can I enable Flutter/Dart language experiments?

Question

I want to use the new spread syntax in Dart.

I'm using Android Studio for Flutter development and I receive this error.

This requires the --spread-collections experiment to be enabled

ListView(children: [...listTiles, MyWidget()])

However, I didn't find anywhere where I could specify this option.

I couldn't even make it work on the command line. flutter --spread-collections run gives Could not find an option named "spread-collections"..

flutter --version
Flutter 1.3.8 • channel beta • https://github.com/flutter/flutter.git
Framework • revision e5b1ed7a7f (4 weeks ago) • 2019-03-06 14:23:37 -0800
Engine • revision f4951df193
Tools • Dart 2.2.1 (build 2.2.1-dev.0.0 571ea80e11)

The experimental features are only on `master` branch. By default you are on `stable` branch. You can see channels using `flutter channel`. Read https://github.com/flutter/flutter/wiki/Flutter-build-release-channels for more info. — Doc, Apr 02 '19 at 18:17
if you still can't get it to work, this worked for me: https://stackoverflow.com/questions/59458433/flutter-flow-control-collections-are-needed-but-are-they — Matjaz Hirsman, Mar 11 '20 at 11:40

atreeon · Accepted Answer · 2021-01-29T10:02:31.537

You need to create an analysis_options.yaml file in the root of your flutter app and write something like

analyzer:
  enable-experiment:
    - spread-collections

Also make sure to switch to the correct channel where the new feature is included eg (dev, beta or master)

flutter channel dev

And also make sure you have a recent enough version of flutter

flutter upgrade

Ensure you are on the right version of flutter and dart that allows that feature by running

flutter --version

you may also have to manually change your pubspec.yaml file to specify the correct dart sdk (if so rerun flutter upgrade)

environment:
  sdk: ">=2.10.0-0 <3.0.0"

Tasnim · Answer 2 · 2020-04-09T13:31:16.263

24

In my case, I have followed these two steps and It worked for me.

run "flutter upgrade"
changing the sdk in the environment in pubspec.yaml
```
environment:
  sdk: ">=2.6.0 <3.0.0"
```

edited Apr 09 '20 at 13:31

answered Mar 06 '20 at 05:50

Tasnim

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9

don't you need to change SDK first and then call "flutter upgrade" – Matjaz Hirsman Mar 11 '20 at 11:39
7

Anyway, you need to remember to restart IDE – sonic Jul 23 '20 at 11:34

score 14 · Answer 3 · answered Jun 02 '20 at 13:48

14

With the new version of flutter it became an error - but it can easily be fixed by updating the sdk version:

environment:
  sdk: ">=2.7.0 <3.0.0"

Just don't forget to restart VisualStudio Code or whatever IDE you're using.

answered Jun 02 '20 at 13:48

C4s4r

404
3
7

score 4 · Answer 4 · edited Apr 07 '20 at 09:07

4

You are running an old version of flutter

Spreading is available starting at flutter 1.5 and dart 2.3

Run:

flutter upgrade

edited Apr 07 '20 at 09:07

Boken

4,825
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answered May 10 '19 at 11:51

ikben

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1

Thanks, please note I asked this questions in April, where Dart 2.3 was not yet available for Flutter in any channels. – Vince Varga May 10 '19 at 11:56
also depends on which flutter channel you are – Matjaz Hirsman Mar 11 '20 at 11:39

score 3 · Answer 5 · answered Apr 29 '20 at 14:35

Here's some fix you can try out :

1) Keep the analysis_options.yaml in your root folder with this code:

analyzer:
  enable-experiment:
    - control-flow-collections

2) Don't use brackets {} in between your for loops Ex:

<Widget>[
  for (final category in categories) 
    CategoryWidget(category: category)
],

3) Important step which is probably why it's not working for you: Change your Dart version constraint in the pubspec.yml file in your root folder to 2.5.2 or above.

environment:
  sdk: ">=2.5.2 <3.0.0"

score 3 · Answer 6 · edited May 18 '20 at 08:46

3

The current answer that is working in the latest Flutter 1.17.1 or Dart 2.8.2

Create a analysis_options.yaml in the directory of the pubspec.yaml file

Write this code inside the file:

include: package:pedantic/analysis_options.1.8.0.yaml 

linter:
  rules:
    - prefer_spread_collections

For more information head to this documentation

edited May 18 '20 at 08:46

Thomas

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answered May 14 '20 at 13:32

Priyansu Choudhury

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10

I Tried it. But I am getting an error 'include: package:pedantic/analysis_options.1.8.0.yaml ' file cannot be found. – Shubham Bansal May 14 '20 at 20:19
@ShubhamBansal You need to add `pedantic: ^1.8.0` to your `dev_dependencies` in `pubspec.yaml`. – Thomas May 18 '20 at 08:46

score 0 · Answer 7 · answered May 28 '20 at 05:15

Something completely different yet the same. Our code was built in Flutter v1.12.13hotfix9. when we did a new installation with flutter 1.17.1 the build broke with a similar error. It seems that the new release of Flutter is not backwards compatible on certain parts. We fixed the problem by installing the older version.

score 0 · Answer 8 · answered Nov 23 '20 at 07:21

0

Run this command from your project's root directory:

dart --enable-experiment=spread-collections lib

answered Nov 23 '20 at 07:21

iDecode

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score 0 · Answer 9 · answered Jan 08 '21 at 09:06

0

After updating the environment in pubspec.yml don't forget restart your IDE

environment:
  sdk: ">=2.7.2 <3.0.0"

answered Jan 08 '21 at 09:06

0xFK

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How can I enable Flutter/Dart language experiments?

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