    //=============================================================================
    //  MuseScore
    //  Music Composition & Notation
    //
    //  Copyright (C) 2008-2011 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 __DURATION_H__
    #define __DURATION_H__

    #include "config.h"
    #include "element.h"
    #include "durationtype.h"

    namespace Ms {

    class Tuplet;
    class Beam;
    class Spanner;

    //---------------------------------------------------------
    //   @@ DurationElement
    ///    Virtual base class for Chord, Rest and Tuplet.
    //
    //   @P duration       Fraction  duration (as written)
    //   @P globalDuration Fraction  played duration
    //---------------------------------------------------------

    class DurationElement : public Element {
          Fraction _duration;
          Tuplet* _tuplet;

    #ifdef SCRIPT_INTERFACE
          Q_GADGET
          Q_PROPERTY(FractionWrapper* duration READ durationW WRITE setDurationW)
          Q_PROPERTY(FractionWrapper* globalDuration READ globalDurW)

          void setDurationW(FractionWrapper* f)  { _duration = f->fraction(); }
          FractionWrapper* durationW() const     { return new FractionWrapper(_duration); }
          FractionWrapper* globalDurW() const    { return new FractionWrapper(globalDuration()); }
    #endif

       public:
          DurationElement(Score* s);
          DurationElement(const DurationElement& e);
          ~DurationElement();

          virtual Measure* measure() const    { return (Measure*)(parent()); }

          virtual bool readProperties(XmlReader& e);
          virtual void writeProperties(XmlWriter& xml) const;
          void writeTuplet(XmlWriter& xml);

          void setTuplet(Tuplet* t)           { _tuplet = t;      }
          Tuplet* tuplet() const              { return _tuplet;   }
          Tuplet* topTuplet() const;
          virtual Beam* beam() const          { return 0;         }
          int actualTicks() const;
          Fraction actualFraction() const;

          virtual Fraction duration() const   { return _duration; }
          Fraction globalDuration() const;
          void setDuration(const Fraction& f) { _duration = f;    }

          virtual QVariant getProperty(P_ID propertyId) const override;
          virtual bool setProperty(P_ID propertyId, const QVariant&) override;
          };

    }     // namespace Ms
    #endif

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