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From: Mycroft Holmes on 25 Feb 2010 05:22
Hi all,

we have a large template-based set of headers; they are pretty much
standard compliant and we cross-compile with VS2005, VS2008, the intel
compiler and some versions of gcc. A few days ago we tested VS2010 RC
and we found the following problems:

(1) if a class has swap(T&) and swap(T&&) then in some cases we cannot
take a pointer to swap(T&).
the following sample shows that in ordinary code, the pointer can be
taken, but in a template it can't.
if you remove AAA::swap(AAA&&) it works.


template <typename T>
void fff(T& x, void (T::*)(T&))
{
}

template <typename T>
void fff(T& x)
{
fff(x, &T::swap);
}



struct AAA
{
void swap(AAA&)
{}

void swap(AAA&&)
{}

};


int main()
{
AAA aa;

void (AAA::*F)(AAA&) = &AAA::swap;

fff(aa);
}




(2) sometimes the compiler is unable to fill-it default template
parameters, and it emits...well... bizarre error messages.
in the sample below, if you write "BBB<this_t, roll_t, LENGTH>" it
works, if you write "BBB<this_t, roll_t>" it does not compile.




template <typename r1_t, typename r2_t, int LENGTH1 = r1_t::length,
int LENGTH2 = r2_t::length>
class BBB;


template <typename r1_t, typename r2_t, int LENGTH>
class BBB<r1_t, r2_t, LENGTH, 1>
{
typedef BBB<r1_t, r2_t, LENGTH, 1> this_t;

public:

BBB(int = 0)
{
}

static const int length = LENGTH;

// bug: VS2010 RC will complain if LENGTH is omitted...
// it says that 'length' is undefined

template <typename roll_t>
inline BBB<this_t, roll_t, LENGTH> operator<<(roll_t) const
{
return 0;
}
};



struct E1
{
static const int length = 1;
};

struct E2
{
static const int length = 2;
};



int main(int argc, const char* argv[])
{
BBB<E2, E1> a;
a << E1();
}



(3) we noticed that in error messages, the "template stack" is not
fully unrolled, so most times it's not easy to understand where
exactly the offending code is. e.g. if you have std::pair<void*,
void*>(0,0) instead of (nullptr,nullptr), most times you'll get an
error ONLY in <utility>, not in the original .cpp, as it happens in
VS2008


From: Igor Tandetnik on 25 Feb 2010 07:56
Mycroft Holmes wrote:
> (1) if a class has swap(T&) and swap(T&&) then in some cases we cannot
> take a pointer to swap(T&).
> the following sample shows that in ordinary code, the pointer can be
> taken, but in a template it can't.
> if you remove AAA::swap(AAA&&) it works.
>
>
> template <typename T>
> void fff(T& x, void (T::*)(T&))
> {
> }
>
> template <typename T>
> void fff(T& x)
> {
> fff(x, &T::swap);
> }

I think the compiler has difficulties with combining overload resolution and template parameter deduction. It does look like a bug to me, I think the code should work as written. As a workaround, try these:

fff<T>(x, &T::swap);
// or
void (T::*F)(T&) = &T::swap;
fff(x, F);
// or
fff(x, static_cast<void (T::*)(T&)>(&T::swap));

> (2) sometimes the compiler is unable to fill-it default template
> parameters, and it emits...well... bizarre error messages.
> in the sample below, if you write "BBB<this_t, roll_t, LENGTH>" it
> works, if you write "BBB<this_t, roll_t>" it does not compile.
>
>
> template <typename r1_t, typename r2_t, int LENGTH1 = r1_t::length,
> int LENGTH2 = r2_t::length>
> class BBB;
>
>
> template <typename r1_t, typename r2_t, int LENGTH>
> class BBB<r1_t, r2_t, LENGTH, 1>
> {
> typedef BBB<r1_t, r2_t, LENGTH, 1> this_t;
>
> public:
>
> BBB(int = 0)
> {
> }
>
> static const int length = LENGTH;
>
> // bug: VS2010 RC will complain if LENGTH is omitted...
> // it says that 'length' is undefined
>
> template <typename roll_t>
> inline BBB<this_t, roll_t, LENGTH> operator<<(roll_t) const
> {
> return 0;
> }
> };

Yes, looks like a bug, too. Comeau accepts this.
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not necessarily a good idea. It is hard to be sure where they are going to land, and it could be dangerous sitting under them as they fly overhead. -- RFC 1925
From: David Lowndes on 25 Feb 2010 09:40
>we have a large template-based set of headers; they are pretty much
>standard compliant and we cross-compile with VS2005, VS2008, the intel
>compiler and some versions of gcc. A few days ago we tested VS2010 RC
>and we found the following problems:

If you feel fairly certain it's a bug, please submit it on the MS
connect web site - that way MS will be aware of it.

Dave
From: Mycroft Holmes on 25 Feb 2010 10:12
On Feb 25, 3:40 pm, David Lowndes <Dav...(a)example.invalid> wrote:
> >we have a large template-based set of headers; they are pretty much
> >standard compliant and we cross-compile with VS2005, VS2008, the intel
> >compiler and some versions of gcc. A few days ago we tested VS2010 RC
> >and we found the following problems:
>
> If you feel fairly certain it's a bug, please submit it on the MS
> connect web site - that way MS will be aware of it.
>
> Dave

I continuously forget the link for bug submissions... can you repost
it here?
TIA
--mh
From: David Lowndes on 25 Feb 2010 10:32
>I continuously forget the link for bug submissions... can you repost
>it here?

connect.microsoft.com

Dave
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