Contents
Contents

Specify type annotations.

This rule is available as of Dart 2.0.0.

This rule has a quick fix available.

Incompatible rules: avoid_types_on_closure_parameters, omit_local_variable_types

Details

#

From the style guide for the flutter repo:

DO specify type annotations.

Avoid var when specifying that a type is unknown and short-hands that elide type annotations. Use dynamic if you are being explicit that the type is unknown. Use Object if you are being explicit that you want an object that implements == and hashCode.

BAD:

dart
var foo = 10;
final bar = Bar();
const quux = 20;

GOOD:

dart
int foo = 10;
final Bar bar = Bar();
String baz = 'hello';
const int quux = 20;

NOTE: Using the the @optionalTypeArgs annotation in the meta package, API authors can special-case type variables whose type needs to by dynamic but whose declaration should be treated as optional. For example, suppose you have a Key object whose type parameter you'd like to treat as optional. Using the @optionalTypeArgs would look like this:

dart
import 'package:meta/meta.dart';

@optionalTypeArgs
class Key<T> {
 ...
}

main() {
  Key s = Key(); // OK!
}

Usage

#

To enable the always_specify_types rule, add always_specify_types under linter > rules in your analysis_options.yaml file:

analysis_options.yaml
yaml
linter:
  rules:
    - always_specify_types