prefer_final_parameters

Prefer final for parameter declarations if they are not reassigned.

This rule is available as of Dart 2.14.0.

This rule has a quick fix available.

Details

DO prefer declaring parameters as final if they are not reassigned in the function body.

Declaring parameters as final when possible is a good practice because it helps avoid accidental reassignments.

BAD:

void badParameter(String label) { // LINT
  print(label);
}

GOOD:

void goodParameter(final String label) { // OK
  print(label);
}

BAD:

void badExpression(int value) => print(value); // LINT

GOOD:

void goodExpression(final int value) => print(value); // OK

BAD:

[1, 4, 6, 8].forEach((value) => print(value + 2)); // LINT

GOOD:

[1, 4, 6, 8].forEach((final value) => print(value + 2)); // OK

GOOD:

void mutableParameter(String label) { // OK
  print(label);
  label = 'Hello Linter!';
  print(label);
}

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

linter:
  rules:
    - prefer_final_parameters