field_initializer_not_assignable

The initializer type '{0}' can't be assigned to the field type '{1}' in a const constructor.

The initializer type '{0}' can't be assigned to the field type '{1}'.

The analyzer produces this diagnostic when the initializer list of a constructor initializes a field to a value that isn't assignable to the field.

The following code produces this diagnostic because 0 has the type int, and an int can't be assigned to a field of type String:

class C {
  String s;

  C() : s = 0;
}

If the type of the field is correct, then change the value assigned to it so that the value has a valid type:

class C {
  String s;

  C() : s = '0';
}

If the type of the value is correct, then change the type of the field to allow the assignment:

class C {
  int s;

  C() : s = 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.