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: 2015-07-26 10:40:02

On 7/26/2015 10:34 AM, Andrey Semashev wrote:
> On 26.07.2015 17:20, Edward Diener wrote:
>> 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.
>>>
>>
>> My latest investigation, using the mpl::size_t code directly in a test,
>> shows that:
>>
>> // size_t_bug.cpp
>>
>> #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;
>> }}
>>
>> #include <boost/core/lightweight_test.hpp>
>> int main()
>> {
>>      return 0;
>> }
>> using namespace boost;
>> using namespace mpl;
>>
>> fails under VC++14 with:
>>
>> size_t_bug.cpp(26): error C2872: 'size_t': ambiguous symbol
>> predefined C++ types (compiler internal)(16): note: could be 'unsigned
>> int size_t'
>> size_t_bug.cpp(6): note: or       'boost::mpl::size_t'
>>
>> but if I comment out the include of lightweight test or if I comment out
>> the using directive, the source compiles without error. How using
>> directives which occur after all code can affect the compilation is
>> beyond me.
>>
>> Anybody who would like to pitch in and try to determine what is causing
>> VC++14 to fail with the above code, which is essentially why it is
>> failing with the MPL tests involving boost::mpl::size_t, please feel
>> free to do so.
>>
>> Needless to say VC++12 and below, as well as gcc and clang, compile the
>> test without error.
>
> This is obviously a compiler bug. Could you report it to MS Connect?
>
> If you're still interested in experimenting, you could try reducing it
> further by, e.g. replacing lightweight_test.hpp with bits of code from
> it, starting from just header includes from lightweight_test.hpp.

Exactly what I intended to do. My experience with MS Connect is that 
unless I can reduce code to something which does not include any 
non-VC++ or non-Windows header they cannot figure out anything or take 
the bug report seriously.