anchor.diff:    visitChildren(Visitor v) {}
   
     bool operator ==(Object other) => other is InvalidType;
  +  int get hashCode => super.hashCode;
   }
   
   class DynamicType extends DartType {
  
positive.code:   bool operator ==(Object other) {
      return other is TypeParameterType && parameter == other.parameter;
    }
  }
  
  /// Declaration of a type variable.
  
negative.code:   visitChildren(Visitor v) {}
  
    bool operator ==(Object other) => other is DynamicType;
  
    int get hashCode => super.hashCode;
  }
  
  class VoidType extends DartType {
  