expected_one_list_pattern_type_arguments

List patterns require one type argument or none, but {0} found.

The analyzer produces this diagnostic when a list pattern has more than one type argument. List patterns can have either zero type arguments or one type argument, but can't have more than one.

The following code produces this diagnostic because the list pattern ([0]) has two type arguments:

void f(Object x) {
  if (x case <int, int>[0]) {}
}

Remove all but one of the type arguments:

void f(Object x) {
  if (x case <int>[0]) {}
}

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.