bootstrapping quantlib

template <class Traits, class Interpolator,
          template <class> class Bootstrap = IterativeBootstrap>
class PiecewiseYieldCurve
    : public Traits::template curve<Interpolator>::type,
      public LazyObject {
  private:
    typedef typename Traits::template curve<Interpolator>::type base_curve;
    typedef PiecewiseYieldCurve<Traits,Interpolator,Bootstrap> this_curve;
    typedef typename Traits::helper helper;
  public:
    typedef Traits traits_type;
    typedef Interpolator interpolator_type;
    PiecewiseYieldCurve(
           Natural settlementDays,
           const Calendar& calendar,
           const std::vector<shared_ptr<helper> >& instruments,
           const DayCounter& dayCounter,
           Real accuracy = 1.0e-12,
           const Interpolator& i = Interpolator());

    // inspectors not shown

    void update();
  private:
    void performCalculations() const;
    DiscountFactor discountImpl(Time) const;
    std::vector<shared_ptr<helper> > instruments_;
    Real accuracy_;

    friend class Bootstrap<this_curve>;
    friend class BootstrapError<this_curve>;
    Bootstrap<this_curve> bootstrap_;
};