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no-runtime-type-to-string

Same as no_runtimeType_toString in Dart lints

Group: Style
Path: lint/style/no-runtime-type-to-string
Default: Off, opt in
Origin: Dart lints
Rule: 295 of 512

Avoid calling toString() on runtimeType.

runtimeType.toString() forces the runtime to keep type names around and is slow; in production builds the names may also be minified:

class Point {
  @override
  String toString() => '$runtimeType()'; // BAD
}

Reported for this.runtimeType, super.runtimeType, or an implicit-this runtimeType getter that is either interpolated or has toString() called on it. Uses inside asserts, throw expressions, catch clauses, mixins, and abstract classes are exempt. Extension-target checks are syntactic: an unqualified named target is checked only if it names a non-abstract class declared in this file, Object, or one of the extension's type parameters. Non-named targets, including dynamic, void, function and record types, are checked. Falcon limitation: other named targets are exempt, including prefixed targets, external classes and Never; this is not a semantic test of whether the target is concrete.

Invalid

example.dartdart

class Point {
  final int x;

  Point(this.x);

  @override
  String toString() => '$runtimeType($x)';

  String describe() => runtimeType.toString();

  String explicit() => this.runtimeType.toString();

  String viaSuper() => super.runtimeType.toString();

  String braced() => 'Instance of ${this.runtimeType}';

  void log() {
    final callback = () => print('$runtimeType');
    callback();
  }
}

enum Color {
  red;

  String label() => '$runtimeType.$name';
}

extension on Point {
  String tag() => runtimeType.toString();
}

class ExplicitDespiteShadow {
  String describe() => this.runtimeType.toString();

  void unrelated(String runtimeType) {}
}

class ExemptionRestoration {
  ExemptionRestoration()
      : assert(runtimeType.toString().isNotEmpty) {
    print('$runtimeType');
  }

  void inspect() {
    try {
      print('$runtimeType');
    } catch (error) {
      print('$runtimeType');
    } finally {
      print('$runtimeType');
    }
    print('$runtimeType');
  }
}

class PrimaryInitializer(int value) {
  this : assert(runtimeType.toString().isNotEmpty);
}

abstract class ExemptBeforeConcrete {
  String describe() => '$runtimeType';
}

class CheckedAfterAbstract {
  String describe() => '$runtimeType';
}

Using `toString` on a `Type` is not safe in production code.

6 @override

7 String toString() => '$runtimeType($x)';

∙

Using `toString` on a `Type` is not safe in production code.

8

9 String describe() => runtimeType.toString();

∙

Using `toString` on a `Type` is not safe in production code.

10

11 String explicit() => this.runtimeType.toString();

∙

Using `toString` on a `Type` is not safe in production code.

12

13 String viaSuper() => super.runtimeType.toString();

∙

Using `toString` on a `Type` is not safe in production code.

14

15 String braced() => 'Instance of ${this.runtimeType}';

∙

Using `toString` on a `Type` is not safe in production code.

17 void log() {

18 final callback = () => print('$runtimeType');

∙

Using `toString` on a `Type` is not safe in production code.

25

26 String label() => '$runtimeType.$name';

∙

Using `toString` on a `Type` is not safe in production code.

29extension on Point {

30 String tag() => runtimeType.toString();

∙

Using `toString` on a `Type` is not safe in production code.

33class ExplicitDespiteShadow {

34 String describe() => this.runtimeType.toString();

∙

Using `toString` on a `Type` is not safe in production code.

41 : assert(runtimeType.toString().isNotEmpty) {

42 print('$runtimeType');

∙

Using `toString` on a `Type` is not safe in production code.

46 try {

47 print('$runtimeType');

∙

Using `toString` on a `Type` is not safe in production code.

50 } finally {

51 print('$runtimeType');

∙

Using `toString` on a `Type` is not safe in production code.

52 }

53 print('$runtimeType');

∙

Using `toString` on a `Type` is not safe in production code.

57class PrimaryInitializer(int value) {

58 this : assert(runtimeType.toString().isNotEmpty);

∙

Using `toString` on a `Type` is not safe in production code.

65class CheckedAfterAbstract {

66 String describe() => '$runtimeType';

∙

Valid

example.dartdart

abstract class Base {
  @override
  String toString() => '$runtimeType';
}

mixin Describe {
  String describe() => runtimeType.toString();
}

class Checked {
  void check(int value) {
    assert(value > 0, '$runtimeType: value must be positive');
    if (value > 10) {
      throw StateError('${runtimeType.toString()} overflow');
    }
    try {
      print(value);
    } catch (e) {
      print('$runtimeType failed: $e');
    }
  }

  String other(Object value) => value.runtimeType.toString();

  String plain() => toString();
}

class Shadowed {
  String describe(String runtimeType) => runtimeType.toString();
}

String topLevel(Object value) => '${value.runtimeType}';

extension on int {
  String tag() => runtimeType.toString();
}

class LaterShadow {
  String describe() => '$runtimeType';

  void unrelated() {
    final runtimeType = 'local';
    print(runtimeType);
  }
}

class InitializerExemptions {
  InitializerExemptions()
      : assert(runtimeType.toString().isNotEmpty, '$runtimeType');
}

// INVALID-CODE: annotation arguments need not be constant for this syntactic rule.
class IgnoredConstructorMetadata {
  @Tag(this.runtimeType.toString())
  IgnoredConstructorMetadata();

  factory IgnoredConstructorMetadata.redirect() =
      Target<void Function(@Tag(this.runtimeType.toString()) int value)>;
}

Configure no-runtime-type-to-string

Set its severity in falcon.json. See the configuration guide.

falcon.jsonjson

{
  "linter": {
    "rules": {
      "style": {
        "no-runtime-type-to-string": "error"
      }
    }
  }
}

Or silence one occurrence with a suppression comment; the reason is required.

example.dartdart

// falcon-ignore lint/style/no-runtime-type-to-string: <reason>

non-constant-identifier-namesnon_constant_identifier_namesrecommended
Flags non-constant identifiers that are not written in lowerCamelCase.
omit-local-variable-typesomit_local_variable_types
Flags local variable type annotations that repeat the initializer's type.
only-throw-errorsonly_throw_errorsrecommended
Only throw instances of classes that extend Exception or Error.
package-namespackage_namesrecommendedcross-file
Require package names to be valid lower_case_with_underscores identifiers.
parameter-assignmentsparameter_assignments
Don't reassign parameters of functions, methods, or constructors.
parameters-ordering
Requires named parameters to follow the explicitly configured alphabetical order.
pattern-fields-ordering
Flags named object and record pattern fields that violate the configured order.
prefer-adjacent-string-concatenationprefer_adjacent_string_concatenationrecommended
Flags two string literals joined with the + operator.