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avoid-default-tostring

v1.30.0
warning
effort: 4m
configurable
teams+

Warns when a class is the target of the toString() invocation, but does not implement toString.

The result of calling toString() on such classes is Instance of ... which is usually not expected.

⚙️ Config​

Set ignore-enums (default is false) to ignore toString() calls on enum constants.

analysis_options.yaml
dcm:
  rules:
    - avoid-default-tostring:
        ignore-enums: false

Example​

❌ Bad:

void fn(SomeClass some) {
  // LINT: The class does not implement 'toString' and will give no meaningful output.
  //  Try implementing 'toString' or replacing with another value.
  some.toString();

  // LINT: The class does not implement 'toString' and will give no meaningful output.
  //  Try implementing 'toString' or replacing with another value.
  print('$some');

  // LINT: The class does not implement 'toString' and will give no meaningful output.
  //  Try implementing 'toString' or replacing with another value.
  [some].toString();
}

class SomeClass {}

✅ Good:

void fn(SomeClass some) {
  some.toString();
  print('$some');
}

class SomeClass {
  @override
  String toString() => 'hi';
}

Additional Resources​

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