[GCC-XML] compilation pb running gccxml on code using SFINAE

[MOSS Sebastian]

Thanks Brad,

Although - as I said after trying this originally - then the value
member can't be used as a template argument:

> macros. I tried the static const approach as well - as I'm using some
> template specializations using has_nested_value_type<>::value - I got
> the complementary error 'non-const type cannot be used as a template
> param'.

i.e.

template <typename T, bool has_nested_value_type = true>
struct register_nested_type
{
    typedef typename register_nested_type< typename T::value_type,
has_nested_value_type<typename T::value_type>::value >::value_type
value_type; 
};

template <typename T>
struct register_nested_type<T, false>
{
    // dumb typedef for termination
    typedef T value_type;
};

Again, this compiles on gcc 3.4 (and not gcc 3.3 or gccxml). Can you
suggest a workaround for this?

Thanks again, in advance,
s

-----Original Message-----
From: Brad King [mailto:brad.king at kitware.com] 
Sent: Wednesday, June 06, 2007 5:33 PM
To: MOSS Sebastian
Cc: gccxml at gccxml.org
Subject: Re: [GCC-XML] compilation pb running gccxml on code using
SFINAE

MOSS Sebastian wrote:
> The code I posted was a complete example in itself - ie no use of
Boost
> macros. I tried the static const approach as well - as I'm using some
> template specializations using has_nested_value_type<>::value - I got
> the complementary error 'non-const type cannot be used as a template
> param'.
>
> So ultimately I guess this is a limitation with gcc3.3 right?

Here is a different implementation that works in gcc versions all the
way back to 2.95:

template <typename T>
struct has_nested_value_type_helper
{
  typedef char (&true_type)[1];
  typedef char (&false_type)[2];
  template <class U> true_type  static impl(typename U::value_type
const*);
  template <class U> false_type static impl(...);
};

template <typename T>
class has_nested_value_type
{
  typedef has_nested_value_type_helper<T> helper;
public:
  static const bool value = (sizeof(helper::template impl<T>(0)) ==
                             sizeof(typename helper::true_type));
};

-Brad 
 
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