Re: [Boost-users] [foreach] gcc 4.5 & 4.6 compiler error with BOOST_FOREACH(auto&& ...) loop

5 Mar 2011

      Sebastian Redl wrote:
...
...
template<typename>
void f()
{
    int A[6];
    for(auto&&  x : A)
        ;
}
Why does this compile? I don't see how any rvalue can be available in that
context.
Wouldn't auto deduction make x an lvalue reference here?
Yes, x should be an lvalue reference here. The code should compile fine.

I think this is a gcc bug.
In a function template, auto deduction fails to deduce an lvalue reference
when auto&& is initiliazed by a function return value of an lvalue reference.

Minimal test case:
(This code fails to be compiled.)

int& identity(int& i)
{
    return i;
}

template  // Commenting this out makes compilation succeed
void f()
{
    int i = 0;
    auto&& x = identity(i); // In a function template, auto deduction fails
}

int main (int argc, char* argv[])
{
    f();
    return 0;
}

Regards,
Michel

Re: [Boost-users] [foreach] gcc 4.5 & 4.6 compiler error with BOOST_FOREACH(auto&& ...) loop

Michel MORIN