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