Subject: Re: [boost] VC10 config - some regressions in several libraries
From: Ion Gaztañaga (igaztanaga_at_[hidden])
Date: 2010-04-29 15:54:49
On 29/04/2010 20:35, Peter Dimov wrote:
> Jeffrey Hellrung:
> ...
>> I'm confused. So static_cast< Arg&& >(r) creates a new temporary
>> object (rather than just a (rvalue) reference to the r object) when
>> used in direct construction, but does not behave this way otherwise
>> (e.g., the line after "//Correct binding" above?
> ...
>> Maybe I don't know rvalue references as well as I had thought... :/
>
> I don't think that casting a T (rvalue or lvalue) to T&& was ever
> supposed to create a temporary; it's always a direct reference binding.
> This is not a rrv1 vs rrv2 issue; it looks like a plain compiler bug.
Compiles fine and prints "6" in GCC 4.5.0
Best,
Ion
#include <iostream>
//store_and_forward_func takes a Target type, catches all references,
//packs them in store_and_forward class, and calls a deferred call
//using the stored arguments:
class int_holder
{
int _i;
public:
int_holder(const int &i)
{ _i = i; }
int_holder(int &&i)
{ _i = i; i = 0; std::cout << _i << std::endl; }
void func(){}
};
template<class Target, class Arg>
struct store_and_forward
{
Arg &&ref; //Stores a reference for further forwarding
store_and_forward(Arg &&r)
: ref(static_cast<Arg&&>(r))
{}
void call()
{
Target a(static_cast<Arg&&>(ref));
a.func();
}
};
template<class Target, class Arg>
void store_and_forward_func(Arg &&r)
{
struct store_and_forward<int_holder, Arg> fwd(static_cast<Arg&&>(r));
fwd.call();
}
int main ()
{
//This should lead to a compilation error
const int & cref = 1;
//Ok
store_and_forward_func<int_holder>(cref);
//Bad forwarding, member reference is not bound
//to the temporary int(6)
store_and_forward_func<int_holder>(int(6));
return 0;
}