sort of dynamic_cast for smart pointers

[nobody]

would not it be cool to have such feature ? so i can 
write
shared_ptr<A> pA=new B();
shared_ptr<B> pB=downcast<B>(pA);

[beman_dawes]

Logged In: YES 
user_id=51042

I'd need to see a more complete proposal before taking any 
action on this one.  You might want to post something on 
the main list.

--Beman

[nobody]

Logged In: NO 

>I'd need to see a more complete proposal before taking any 
>action on this one.  You might want to post something on 
>the main list.
Sorry, i don't know what 'main list' is, so i'll try to 
explain here.
In two words, i want a function with signature
template <class To,class From>
smart_ptr<To> downcast(smart_ptr<From>)
which will attempt to cast From* to To* (the way 
dynamic_cast doing this) and will return smart_ptr<To> 
sharing same reference count with smart_ptr<From> in case 
of success. If the cast is illegal, the function will 
return null-smart_ptr<To>.
For me, such a function is very convenient and absolutely 
necessary in some cases.