Re: [Quantlib-dev] Array vs std::vector + free operators

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

On Thu, 2007-04-19 at 15:47 +0200, DU VIGNAUD DE VILLEFORT FRANCOIS
GASAPRD PHI wrote:
> I have tried to removing the dependency on Array class from the
> optimization framework. One change leading to another it turns out
> that Arrray dependencies could be removed in the whole QL !
> The only change I had to do was to provide missing operators an
> independent header file and all worked fine. As a result I’m wondering
> if using plain std::vector instead of Arrray wouldn’t be more
> efficient in terms of compilation efficiency and flexibility of use.
> (if one want to use linear algebra he has just to include a file
> defining new operators…).

François,
	it doesn't sound right to me, for a couple of reasons:

- you're changing the std::vector interface by adding operators. I'm not
sure that it is legal C++.  Moreover, this might be done without the
user knowing it if he happens to include a file which in turn includes
your new operators. Thus, code which according to the C++ standard is
not valid (such as w = u+v if u,v,and w are std::vectors) would silently
become legal. I'm not comfortable with this.

- there's a conceptual difference between the two classes, and using
std::vector for both would confuse the issue. std::vector is a
container; Array is the linear-algebra concept of an array. I, too, had
been thinking of replacing Array with an STL class, but the right one
would be std::valarray---which models the right concept and already
defines the required operators.

Later,
	Luigi


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