Re: [boost] Another numeric_cast sepcialization problem

From: Peter Dimov (pdimov_at_[hidden])
Date: 2001-10-31 10:50:33

From: <helmut.zeisel_at_[hidden]>
> Should the following program compile?
> GCC 3.0.1 says 

[ambiguity]

> Is GCC right?

Unfortunately yes. This is an open issue (CWG #214 IIRC.)

> If yes, is there any other way
> to this partial specialization/overload?

Use the helper class template trick:

template<class Out, class In> struct numeric_cast_helper
{
 Out operator()(In in) const { return in; }
};

template<typename Out, typename In> Out numeric_cast(In in)
{
  return numeric_cast_helper<Out, In>()(in);
}

template<typename Digit>
class my_int {};

template<typename Digit> struct numeric_cast_helper<my_int<Digit>, double>
{
 my_int<Digit> operator()(double arg)
 {
  return my_int<Digit>();
 }
};

int main()
{
 double a=5;

 my_int<int> j=numeric_cast<my_int<int> >(a);

 return 0;
}

--
Peter Dimov
Multi Media Ltd.