redirect_to_invalid_return_type

The return type '{0}' of the redirected constructor isn't a subtype of '{1}'.

The analyzer produces this diagnostic when a factory constructor redirects to a constructor whose return type isn't a subtype of the type that the factory constructor is declared to produce.

The following code produces this diagnostic because A isn't a subclass of C, which means that the value returned by the constructor A() couldn't be returned from the constructor C():

class A {}

class B implements C {}

class C {
  factory C() = A;
}

If the factory constructor is redirecting to a constructor in the wrong class, then update the factory constructor to redirect to the correct constructor:

class A {}

class B implements C {}

class C {
  factory C() = B;
}

If the class defining the constructor being redirected to is the class that should be returned, then make it a subtype of the factory's return type:

class A implements C {}

class B implements C {}

class C {
  factory C() = A;
}

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