[boost] [type_traits] fully qualified names

From: Jody Hagins (jody-boost-011304_at_[hidden])
Date: 2005-03-10 16:39:11

The coding guidelines document (boost/more/int_const_guidelines.htm),
states the following...

Always use a fully qualified name to refer to an integral constant
expression.

For example:

typedef myclass< ::boost::is_integral<some_type>::value> mytypedef;

Rationale: at least one compiler (Borland's), doesn't recognise the name
of a constant as an integral constant expression unless the name is
fully qualified (which is to say it starts with ::).

However, it appears that the same compiler (BCB6) has problems if the
'::' is left in.  For example...

template <class T>
struct Foo
{
  typedef typename ::boost::remove_reference< T >::type type;
  typedef typename ::boost::add_reference<
      typename ::boost::add_const< type >::type
      >::type ref_to_const_type;
};

fails to compile.  Initially I thought it had something to do with
typename (e.g., another BOOST_DEDUCED_TYPENAME) because, the first,
simpler line compiles if I remove the "typename" keyword. 
Unfortunately, the following does not compile either

template <class T>
struct Foo
{
  typedef          ::boost::remove_reference< T >::type type;
  typedef          ::boost::add_reference<
               ::boost::add_const< type >::type
      >::type ref_to_const_type;
};

After seeing a notice on this list a few minutes ago, I decided to
remove the '::' and whaddya know...

template <class T>
struct Foo
{
  typedef typename boost::remove_reference< T >::type type;
  typedef typename boost::add_reference<
      typename boost::add_const< type >::type
      >::type ref_to_const_type;
};

this compiles correctly.

So, I am left scratching my head, wondering what to do if I want to use
TypeTraits in a portbale manner.

Thanks!