omit_local_variable_types

Omit type annotations for local variables.

This rule is available as of Dart 2.0.0.

This rule has a quick fix available.

Incompatible rules: always_specify_types

Details

DON’T redundantly type annotate initialized local variables.

Local variables, especially in modern code where functions tend to be small, have very little scope. Omitting the type focuses the reader’s attention on the more important name of the variable and its initialized value.

BAD:

List<List<Ingredient>> possibleDesserts(Set<Ingredient> pantry) {
  List<List<Ingredient>> desserts = <List<Ingredient>>[];
  for (final List<Ingredient> recipe in cookbook) {
    if (pantry.containsAll(recipe)) {
      desserts.add(recipe);
    }
  }

  return desserts;
}

GOOD:

List<List<Ingredient>> possibleDesserts(Set<Ingredient> pantry) {
  var desserts = <List<Ingredient>>[];
  for (final recipe in cookbook) {
    if (pantry.containsAll(recipe)) {
      desserts.add(recipe);
    }
  }

  return desserts;
}

Sometimes the inferred type is not the type you want the variable to have. For example, you may intend to assign values of other types later. In that case, annotate the variable with the type you want.

GOOD:

Widget build(BuildContext context) {
  Widget result = Text('You won!');
  if (applyPadding) {
    result = Padding(padding: EdgeInsets.all(8.0), child: result);
  }
  return result;
}

Usage

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

linter:
  rules:
    - omit_local_variable_types