one thing that bugs me about c++

[guslay]

Neal Becker Wrote:

> --------------------
> #include <complex>
> #include <vector>
> 
> using namespace std;
> 
> template<typename T>
> T mag_sqr1 (T z) { return z * z; }
> 
> template<typename T>
> T mag_sqr1 (complex<T> z) { return real(z)*real(z) + imag(z)*imag(z); }
> 
> template<typename T>
> struct scalar { typedef T type; };
> 
> template<typename T>
> struct scalar<complex<T> > { typedef T type; };
> 
> 
> template<typename T>
> inline vector<typename scalar<T>::type> mag_sqr (vector<T> const& z) {
>   typedef typename scalar<T>::type out_t;
>   vector<out_t> out (z.size());
>   std::transform (z.begin(), z.end(), out.begin(), mag_sqr1<T>);
>   return out;
> }
> 
> int main () {
>   vector<complex<double> > v;
>   mag_sqr (v);
> }


The instantiation capability within std::transform appears to be the limitation. Who knows why. If you do it in two steps, by first defining a function pointer, it works fine for complex and double.

  out_t (*ptrF)(T) = &mag_sqr1;
  std::transform (z.begin(), z.end(), out.begin(), ptrF );

I will leave the implementation in D to someone else, but I bet it would look better.