prefer_final_locals

Prefer final for variable declarations if they are not reassigned.

DO prefer declaring variables as final if they are not reassigned later in the code.

Declaring variables as final when possible is a good practice because it helps avoid accidental reassignments and allows the compiler to do optimizations.

BAD:

void badMethod() {
  var label = 'hola mundo! badMethod'; // LINT
  print(label);
}

GOOD:

void goodMethod() {
  final label = 'hola mundo! goodMethod';
  print(label);
}

GOOD:

void mutableCase() {
  var label = 'hola mundo! mutableCase';
  print(label);
  label = 'hello world';
  print(label);
}

The prefer_final_locals rule is incompatible with the following rules:

• unnecessary_final

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

linter:
  rules:
    - prefer_final_locals

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

linter:
  rules:
    prefer_final_locals: true

Unless stated otherwise, the documentation on this site reflects Dart 3.6.0. Page last updated on 2025-01-27. View source or report an issue.