prefer_final_parameters

Prefer final for parameter declarations if they are not reassigned.

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);
}

The prefer_final_parameters rule is incompatible with the following rules:

• unnecessary_final
• avoid_final_parameters

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

If you're instead using the YAML map syntax to configure linter rules, add prefer_final_parameters: true under linter > rules:

linter:
  rules:
    prefer_final_parameters: true