for_in_of_invalid_element_type

The type '{0}' used in the 'for' loop must implement '{1}' with a type argument that can be assigned to '{2}'.

The analyzer produces this diagnostic when the Iterable or Stream in a for-in loop has an element type that can't be assigned to the loop variable.

The following code produces this diagnostic because <String>[] has an element type of String, and String can't be assigned to the type of e (int):

void f() {
  for (int e in <String>[]) {
    print(e);
  }
}

If the type of the loop variable is correct, then update the type of the iterable:

void f() {
  for (int e in <int>[]) {
    print(e);
  }
}

If the type of the iterable is correct, then update the type of the loop variable:

void f() {
  for (String e in <String>[]) {
    print(e);
  }
}

Unless stated otherwise, the documentation on this site reflects Dart 3.7.3. Page last updated on 2025-05-08. View source or report an issue.