[boost] Re: Re: Boost.Variant collaboration effort

From: Itay Maman (itay_maman_at_[hidden])
Date: 2002-07-21 11:23:07

"David Abrahams" <david.abrahams_at_[hidden]> wrote in message
news:138c01c230bc$cbe3bd00$6501a8c0_at_boostconsulting.com...
> From: "Douglas Gregor" <gregod_at_[hidden]>
>
>
[snip]
>
> That was my understanding also. Incidentally, I recently implemented
> extract<> for Boost.Python.
>
> extract<> is a class template which admits the following uses:
>
>     int y = extract<int>(x);
>     extract<int> xint((z));
>
>     if (xint.check())
>     {
>         int i = xint();
>         ...
>     }
>     return extract<foo&>(z);
>
> I realize that poses some problems for unification, since it's not
possible
> to non-intrusively customize constructors for a single class template. I'm
> willing to discuss changes, if neccessary.
>
> -Dave
>

(i) Is it in the CVS?

(ii) There's this MSVC namespace-related bug, which makes it impossible to
use extract<T>(x). The workaround I have used so far, is to pass T as a
dummy parameter, i.e: extract(x, boost::type<T>());
I wonder if there are other workarounds which will not affect the interface
of the function?

The program below illustrates the problem. When *1* is uncommented
everything is fine, but if *2* is active, the compiler stops:
"main.cpp(23) : error C2062: type 'int' unexpected"

#include <iostream>

namespace test_site
{

template<typename R>
void func(short )
{ 
   std::cout << "Hi" << std::endl;
}

} // namespace test_site

int main()
{
   // using namespace test_site;  // *1*  - Ok on MSVC6
   using test_site::func;        // *2*  - Err on MSVC6

   func<int>(0);

   return 0;
}