is_a<> with references

[Aldy Hernandez via Gcc]

Hi folks.

I rolled our own is_a<> implementation for vrange, because it was
trivial.  We needed it to work on references, and GCC's is-a.h
implementation is pointer-only. However, I now realize it confuses
gengtype when adding additional types:

template<typename T>
struct vrange_traits
{
  // Default to something unusable.
  typedef void range_type;
};

template<>
struct vrange_traits<irange>
{
  typedef irange range_type;
};

template<>
struct vrange_traits<frange>
{
  typedef frange range_type;  <-- BOO! HISS!
};

build/gengtype  \
                    -S /home/aldyh/src/gcc/gcc -I gtyp-input.list -w
tmp-gtype.state
/home/aldyh/src/gcc/gcc/value-range.h:291: type `range_type' previously defined
/home/aldyh/src/gcc/gcc/value-range.h:285: previously defined here

Can some gengtype guru offer guidance?

Thanks.
Aldy