Re: [boost] [mpl] Problem with VC++14 and boost::mpl::size_t

Subject: Re: [boost] [mpl] Problem with VC++14 and boost::mpl::size_t
From: Edward Diener (eldiener_at_[hidden])
Date: 2015-07-25 16:34:14

On 7/25/2015 2:48 AM, Matt Calabrese wrote:
> On Fri, Jul 24, 2015 at 7:41 PM, Edward Diener <eldiener_at_[hidden]>
> wrote:
>
>> pointing to the line after it encounters 'struct size_t' as far as I can
>> make out ( you need to preprocess the size_t.cpp test, comment out the
>> #line directives and run the test against the preprocessed result to see
>> what the compiler is objecting to ). It therefore fails a number of mpl
>> tests which all prior versions of VC++ pass.
>>
>> It flags this error in 5 mpl tests which use the boost::mpl::size_t
>> integral wrapper, among which the easiest to analyze is the size_t.cpp test
>> itself.
>>
>> Anybody have any idea what is going on here with the compiler, or whether
>> it can be fixed somehow in VC++14 for the mpl code ?
>>
>
> I don't have the compiler, but my guess is it's probably actually confused
> on the line:
>
> typedef size_t type;
>
> A simple workaround to try could be to change the typedef to:
>
> typedef mpl::size_t<N> type;
>
> If that fix works, I'd be surprised if such a change would break any other
> compilers. This is all just a guess, though.
>

Actually this program, which is what the boost::mpl::size_t outputs as 
in VC++14, compiles without error in VC++14:

#include <cstddef>
namespace boost { namespace mpl {
struct integral_c_tag { static const int value = 0; };
template< std::size_t N >
struct size_t
{
     static const std::size_t value = N;
     typedef size_t type;
     typedef std::size_t value_type;
     typedef integral_c_tag tag;
     typedef boost::mpl::size_t< static_cast<std::size_t>((value + 1)) > 
next;
     typedef boost::mpl::size_t< static_cast<std::size_t>((value - 1)) > 
prior;
     operator std::size_t() const { return 
static_cast<std::size_t>(this->value); }
};
template< std::size_t N >
std::size_t const boost::mpl::size_t< N >::value;
}}

int main()
{
return 0;
}

So why the MPL tests which use boost::mpl::size_t are failing is still a 
mystery to me. When the error message shows in the size_t test it says:

size_t.cpp(30): error C2872: 'size_t': ambiguous symbol
predefined C++ types (compiler internal)(16): note: could be 'unsigned 
int size_t'
C:\Programming\VersionControl\modular-boost\boost/mpl/aux_/integral_wrapper.hpp(44): 
note: or       'boost::mpl::size_t'

but the first line of the error message is pointing to the last empty 
line of size_t.cpp. If I preprocess the file and then test the 
preprocessed file, the error message is:

size_t_ii.cpp(68259): error C2872: 'size_t': ambiguous symbol
predefined C++ types (compiler internal)(16): note: could be 'unsigned 
int size_t'
size_t_ii.cpp(16566): note: or       'boost::mpl::size_t'

but here the first line of the error message is pointing to one beyond 
the last line of the preprocessed file.