Re: [boost] [1.33.0] VC 7.1 vs. SFINAE/type traits

From: Thomas Witt (witt_at_[hidden])
Date: 2005-08-16 17:54:08

Mat,

Mat Marcus wrote:
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> In one of our projects, the following code produces some strange
> compilation errors under VC 7.1/boost 1.33.0. Can anyone suggest a
> workaround?
> 
>  - Mat
> 
> #include <sstream>
> #include "boost/type_traits.hpp"
> #include "boost/utility/enable_if.hpp"
> 
> template <typename EnumType>
> typename boost::enable_if<boost::is_enum<EnumType>, EnumType>::type 
> operator ~ (EnumType a);

I can't say whether that is your problem, but code like this is 
potentially dangerous. It'll break whenever you happen to "suck" in a 
use of operator~ on an unnamed enum. And yes it tends to generate weird 
error messages. Looking at the errors the unknown type in the is_enum 
instantiation looks suspicious to me.

I only have apples gcc 4 currently. A slightly modified example gives this:

enum { foo, bar };

template <typename EnumType>
typename boost::enable_if<boost::is_enum<EnumType>, EnumType>::type
operator ~ (EnumType a);

int main()
{

   int i = ~bar;

std::stringstream t;

}

mat.cpp: In function 'int main()':
mat.cpp:14: error: '<anonymous enum>' is/uses anonymous type
mat.cpp:14: error:   trying to instantiate 'template<class T> struct 
boost::is_enum'

Thomas

> 
> std::stringstream t;
> 
> 
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