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avoid-ignoring-return-values

added in: 1.6.0
warning
Pro+

Warns when a return value of a method or function invocation or a class instance property access is not used.

Silently ignoring such values may lead to a potential error especially when the invocation target is an immutable instance which has all its methods returning a new instance (for example, String or DateTime classes).

Example​

❌ Bad:

int foo() {
  return 5;
}

void bar() {
  print('whatever');
}

void main() {
  bar();
  foo(); // LINT: Avoid ignoring return values.

  final str = "Hello there";
  str.substr(5); // LINT: Avoid ignoring return values.

  final date = new DateTime(2018, 1, 13);
  date.add(Duration(days: 1, hours: 23)); // LINT: Avoid ignoring return values.
}

✅ Good:

int foo() {
  return 5;
}

void bar() {
  print('whatever');
}

void main() {
  bar();
  final f = foo(); // Correct, return value is assigned  
  
  final str = "Hello there";
  final newString = str.substr(5);  
  
  final date = new DateTime(2018, 1, 13);
  final newDate = date.add(Duration(days: 1, hours: 23));
}