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avoid-mutating-parameters

added in: 1.7.0
warning
Pro+

Warns when a parameter's field or setter is reassigned.

Mutating fields of complex parameter objects can lead to unexpected results (for example, when one function changes the passed object in a way that affects the outer function's result) and reduce readability and maintainability of the code.

Example​

❌ Bad:

class SomeClass {
  var flag = true;

  set value(String value) {
    ...
  }
}

void function(SomeClass some) {
  some.flag = false; // LINT: Avoid mutating parameters.
  some.value = 'hello'; // LINT: Avoid mutating parameters.
}

✅ Good:

class SomeClass {
  var flag = true;

  set value(String value) {
    ...
  }
}

SomeClass function(SomeClass some) {
  final newValue = SomeClass();
  newValue.flag = false;
  newValue.value = 'hello';

  return newValue; // Correct, returning a new object instead
}