#ifndef CELL_H#define CELL_H#include <QTableWidgetItem>class Cell : public QTableWidgetItem{public:    Cell();    QTableWidgetItem *clone() const;    void setData(int role, const QVariant &value);    QVariant data(int role) const;    void setFormula(const QString &formula);    QString formula() const;    void setDirty();private:    QVariant value() const;    QVariant evalExpression(const QString &str, int &pos) const;    QVariant evalTerm(const QString &str, int &pos) const;    QVariant evalFactor(const QString &str, int &pos) const;    mutable QVariant cachedValue;    mutable bool cacheIsDirty;};#endif