cast_from_nullable_always_fails

This cast will always throw an exception because the nullable local variable '{0}' is not assigned.

The analyzer produces this diagnostic when a local variable that has a nullable type hasn't been assigned and is cast to a non-nullable type. Because the variable hasn't been assigned it has the default value of null, causing the cast to throw an exception.

The following code produces this diagnostic because the variable x is cast to a non-nullable type (int) when it's known to have the value null:

void f() {
  num? x;
  x as int;
  print(x);
}

If the variable is expected to have a value before the cast, then add an initializer or an assignment:

void f() {
  num? x = 3;
  x as int;
  print(x);
}

If the variable isn't expected to be assigned, then remove the cast:

void f() {
  num? x;
  print(x);
}

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.