Re: [boost] VC10 config - some regressions in several libraries

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;
}