Re: [Quantlib-dev] a simple question

[Luigi B. <lui...@gm...>]

On Fri, 2007-05-18 at 15:00 +0200, DU VIGNAUD DE VILLEFORT FRANCOIS
GASAPRD PHI wrote:
> >As for QL_NULL_REAL, it doesn't really matter what value is used as long as >it's a determined one
> 
> Since it is now used as some kind of unitialized value by the quotes classes, I would say that it is no longer such an immaterial detail.

Sure. We picked a value which is unlikely to be chosen as a valid one;
but since it has to be a value anyway (we could use NaN, but it's not
very portable) it's not foolproof.

> Maybe you have thought about boost::optional for the same reason. ;-) 
> It would be cleaner indeed. However I'm not convinced that it's a good solution yet.
> IMO boost::optional a pefect solution in the case of a free function which can return invalid result even in normal situations. (like the second example of boost optional tutorial).
> 
> On the hand it seems to me that using it for a function member would add some spurious trickyness to the class. What do you think of this implementation ? 
> 
> 	Quote():isValid_(false){}
> 
> 	virtual void resetQuote() {
> 	    isValid_ = false;
> 	}
> 
> 	virtual bool isValid() const {
> 	    return isValid_;
> 	};
> 	private:
> 	bool isValid_;

Is this the base class? In this case, isValid_ should be protected and
derived classes would have to manage it. Using optional wouldn't be so
tricky: we could just write SimpleQuote as (without namespace boost)

class SimpleQuote {
  private:
    optional<Real> value_;
  public:
    explicit SimpleQuote(optional<Real> value = none)
    : value_(value) {}

    bool isValid() const {
        return value_;  // automatic conversion to bool
    }

    Real value() const {
        return *value_; // access the actual Real
    }

    Real setValue(Real x) {
        value_ = x;     automatic conversion to optional
        ... // notify etc.
    }
};

SimpleQuote q1;       // not initialized, isValid() returns false
SimpleQuote q2(42.0); // double automatically converted to optional

Later,
	Luigi




---------------------------------------- 

The First Rule of Optimization: Don't do it. 
The Second Rule of Optimization (For experts only): Don't do it yet. 
-- Michael Jackson