default_value_in_redirecting_factory_constructor

Default values aren't allowed in factory constructors that redirect to another constructor.

The analyzer produces this diagnostic when a factory constructor that redirects to another constructor specifies a default value for an optional parameter.

The following code produces this diagnostic because the factory constructor in A has a default value for the optional parameter x:

class A {
  factory A([int x = 0]) = B;
}

class B implements A {
  B([int x = 1]) {}
}

Remove the default value from the factory constructor:

class A {
  factory A([int x]) = B;
}

class B implements A {
  B([int x = 1]) {}
}

Note that this fix might change the value used when the optional parameter is omitted. If that happens, and if that change is a problem, then consider making the optional parameter a required parameter in the factory method:

class A {
 factory A(int x) = B;
}

class B implements A {
  B([int x = 1]) {}
}

Unless stated otherwise, the documentation on this site reflects Dart 3.8.0. Page last updated on 2025-05-08. View source or report an issue.