Re: QuEP 4: Reducing abstraction penalty by means of disposable arrays

Posted by Luigi Ballabio on May 17, 2006; 2:23am
URL: http://quantlib.414.s1.nabble.com/QuEP-4-Reducing-abstraction-penalty-by-means-of-disposable-arrays-tp11132p11133.html

On 05/16/2006 07:52:59 PM, DU VIGNAUD François wrote:
> The following constructor destroys
> the non disposable object t given as argument:
> (ql/Utilities/disposable.hpp)
>
>     template <class T>
>     inline Disposable<T>::Disposable(T& t) {
>         this->swap(t);
>     }

Yes, this is by design. The purpose is to allow one to write

Disposable<Foo> bar() {
     Foo f(1,2);
     return f;
}

and avoid the copy in the automatic conversion from Foo to  
Disposable<Foo> implied by the return. The problem was that it is  
difficult to initialize a Disposable directly, as in:

Disposable<Foo> baz() {
     Disposable<Foo> f(1,2);
     return f;
}

because Disposable has no idea of how many arguments the constructor  
should take, nor of their types. Other approaches might be possible,  
but I think they make the resulting client code more clumsy.

Luigi


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The first rule of intelligent tinkering is to save all the parts.
-- Paul Erlich