no_runtimeType_toString

Avoid calling toString() on runtimeType.

Calling toString on a runtime type is a non-trivial operation that can negatively impact performance. It's better to avoid it.

BAD:

class A {
  String toString() => '$runtimeType()';
}

GOOD:

class A {
  String toString() => 'A()';
}

This lint has some exceptions where performance is not a problem or where real type information is more important than performance:

• in an assertion
• in a throw expression
• in a catch clause
• in a mixin declaration
• in an abstract class declaration

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

linter:
  rules:
    - no_runtimeType_toString

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

linter:
  rules:
    no_runtimeType_toString: true

Unless stated otherwise, the documentation on this site reflects Dart 3.6.2. Page last updated on 2025-01-27. View source or report an issue.