    //=============================================================================
    //  MuseScore
    //  Music Composition & Notation
    //
    //  Copyright (C) 2002-2011 Werner Schweer
    //
    //  This program is free software; you can redistribute it and/or modify
    //  it under the terms of the GNU General Public License version 2
    //  as published by the Free Software Foundation and appearing in
    //  the file LICENCE.GPL
    //=============================================================================

    #ifndef __NOTELINE_H__
    #define __NOTELINE_H__

    #include "textlinebase.h"

    namespace Ms {

    class Note;

    #if 0
    //---------------------------------------------------------
    //   @@ TextLineSegment
    //---------------------------------------------------------

    class TextLineSegment : public TextLineBaseSegment {
          Q_GADGET

       protected:

       public:
          TextLineSegment(Score* s) : TextLineBaseSegment(s)  { }
          virtual ElementType type() const override     { return ElementType::TEXTLINE_SEGMENT; }
          virtual TextLineSegment* clone() const override { return new TextLineSegment(*this); }
          TextLine* textLine() const                      { return (TextLine*)spanner(); }
          virtual void layout() override;
          virtual QVariant getProperty(P_ID propertyId) const override;
          virtual bool setProperty(P_ID propertyId, const QVariant&) override;
          virtual QVariant propertyDefault(P_ID) const override;
          virtual PropertyStyle propertyStyle(P_ID) const override;
          virtual void resetProperty(P_ID id) override;
          virtual void styleChanged() override;
          };
    #endif

    //---------------------------------------------------------
    //   @@ NoteLine
    //---------------------------------------------------------

    class NoteLine : public TextLineBase {
          Q_GADGET

          Note* _startNote;
          Note* _endNote;

       public:
          NoteLine(Score* s);
          NoteLine(const NoteLine&);
          ~NoteLine() {}

          virtual NoteLine* clone() const           { return new NoteLine(*this); }
          virtual ElementType type() const        { return ElementType::NOTELINE; }

          void setStartNote(Note* n)  { _startNote = n; }
          Note* startNote() const     { return _startNote; }
          void setEndNote(Note* n)    { _endNote = n; }
          Note* endNote() const       { return _endNote; }
          virtual LineSegment* createLineSegment() override;
          };

    }     // namespace Ms
    #endif

↑ V690 The 'NoteLine' class implements a copy constructor, but lacks the '=' operator. It is dangerous to use such a class.