duplicate_pattern_field

The field '{0}' is already matched in this pattern.

The analyzer produces this diagnostic when a record pattern matches the same field more than once, or when an object pattern matches the same getter more than once.

The following code produces this diagnostic because the record field a is matched twice in the same record pattern:

void f(({int a, int b}) r) {
  switch (r) {
    case (a: 1, a: 2):
      return;
  }
}

The following code produces this diagnostic because the getter f is matched twice in the same object pattern:

void f(Object o) {
  switch (o) {
    case C(f: 1, f: 2):
      return;
  }
}
class C {
  int? f;
}

If the pattern should match for more than one value of the duplicated field, then use a logical-or pattern:

void f(({int a, int b}) r) {
  switch (r) {
    case (a: 1, b: _) || (a: 2, b: _):
      break;
  }
}

If the pattern should match against multiple fields, then change the name of one of the fields:

void f(({int a, int b}) r) {
  switch (r) {
    case (a: 1, b: 2):
      return;
  }
}

Unless stated otherwise, the documentation on this site reflects Dart 3.8.1. Page last updated on 2025-05-08. View source or report an issue.