Re: [boost] Re: Perfect Forwarding (almost)

From: Daniel Wallin (dalwan01_at_[hidden])
Date: 2004-02-11 18:32:07

Powell, Gary wrote:
> Nice.  I think we'd implement a "move" function which could handle
> that explicitly in any real implementation:
> 
>     Y(ref rhs)
>       : X( move(*rhs.p) ) // <== here
>       , id(++cnt)
>       , owner(rhs.p->owner)
>     {
>         std::cout << "MOVE #" << id << " <== #" << rhs.p->id << std::endl;
>         rhs.p->owner = false;
>         assert(owner);
>     }
> ==========================================
> Gary > Thank you!
> 
> I must be dense but I'm not seeing how a move function would give us
> the right type.
> 
> template<class T>
> ??? move(T &)
> {... }
> 
>     X( move (*rhs.p) )   // T is a Y 
>                          // calls X copy if move returns T *.
> 
> and we need
> 
>     X ( X::ref)  // and X::ref only takes a X * and X::ref private to X.
> 
> What am I missing here?

That ref doesn't need to be private in X?

   template<class T> rvalue_ref<T> move(T&);

> ==========================================
> 
>>All in all
>>I like it better than the MOJO soln which IMO was much more
>>invasive. 
> 
> 
> What about the MOJO approach seems more invasive to you?
> ===========================================
> Gary > Well you need to modify both the functions you use and the class. 
> And the class requires more modification.

It's only more modification because you added a whole lot of assignment
operators, it's not like the generated one will do the right thing with
the new approach.

> // Special return type from an object to use it....
> // test with binary operator +
> ::mojo::fnresult<Y> operator +(Y lhs, Y const &rhs) {
>     return lhs; // do the addition here
> }
> 
> vs with move.cpp, no special type necessary....
> Y operator + (Y lhs, Y const &rhs){
>    return lhs; // do the addition here.
> }

fnresult is only used to work around the rvalue to const& binding
problem. I'm not sure I understand what Rani has been saying, but it
seems like whatever applies here would apply to Mojo as well. So AFAICT:
if it works with Dave's code, it should work with Mojo. I might as well
be wrong though.

BTW, your quoting style is _really_ annoying. Please try to use standard
quoting.

-- 
Daniel Wallin