Subject: Re: [boost] [config] vc10 and BOOST_NO_DECLTYPE
From: Eric Niebler (eric_at_[hidden])
Date: 2010-04-06 15:58:59
On 4/6/2010 12:49 PM, Eric Niebler wrote:
> The issue is whether the decltype keyword is too broken on VC10 to
> define BOOST_NO_DECLTYPE. I think it /may/ be, so we should define it
> just to be safe, at least for 1.43.
>
Actually, I may have been too hasty. I notice the same behavior on
recent gcc builds. That is, the following program causes both vc10 and
gcc in std=c++0x mode to run out of heap space.
template<class T>
struct S;
template<class X, class Y> struct pair {};
template<class T>
S<T> wrap(T) { return 0; }
template<class T>
struct S
{
S(int = 0) {}
// The following use of decltype causes the compiler to blow up:
decltype(wrap(pair<T,T>())) foo() { return wrap(pair<T,T>()); }
// The following, which should be equivalent, compiles without
// problem:
//S<pair<T,T> > foo() { return wrap(pair<T,T>()); }
};
int main()
{
S<int> s;
}
If these are both conforming implementations of decltype, that's bad
news. It means that std::result_of has a significant and unfortunate
change of behavior from tr1::result_of and boost::result_of, and also
means that decltype cannot be safely used in all contexts.
I think we need a decltype expert to weigh in on this. I may bring the
issue up with the std committee.
-- Eric Niebler BoostPro Computing http://www.boostpro.com