Re: [Quantlib-dev] Disposable doesn't work?

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

On Fri, 2010-12-03 at 11:45 -0500, Kakhkhor Abdijalilov wrote:
> Disposable template is supposed to eliminate unnecessary copy
> construction when returning temporal objects from functions. On my
> platform it actually prevents RVO (elide optimization) and triggers
> copy construction, whereas without Disposable RVO eliminates
> unnecessary copy construction.
> 
> Explicit assignment triggers copying with or without Disposable.

Of course it triggers assignment.  Your class must support Disposable
for it to work fully (see, e.g., the Array class.)  In your case, it
should be something like

struct A {
    A() {}
    A(const A&) { cout << "Triggered copy ctor A(const A&)\n"; }
    A(const Disposable<A>& a) { swap(const_cast<Disposable<A>&>(a)); }

    A& operator=(const A&) {
        cout << "Triggered assignment A::=\n";
        return *this;
    }
    A& operator=(const Disposable<A>& a) {
        swap(const_cast<Disposable<A>&>(a));
        return *this;
    }

    void swap(A&) {}
};

Hopefully, in a few years all compilers will support C++0X and we'll be
able to use rvalue references instead... (your class will still have to
support them. though.)

Luigi


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