Template specialization by another template (of same class)

Question

I'm writing an array class. This array class can contain again arrays as members. When implementing a printing function, I need specializations.

26:template <class T> class array : public vector<T>{
public:
    ...
       string* printToString();
    ...
};
...           
template <class T> string* array<T>::printToString(){
   ...  // generic function
}
template <> inline string* array<double>::printToString(){
   ...  // spezialization for double, works
}
561:template <class U> string* array<array<U>*>::printToString(){
   ...  // does not work
}

The last definition produces

src/core/array.h:561: error: invalid use of incomplete type ‘class array<array<T> >’
src/core/array.h:26: error: declaration of ‘class array<array<T> >’

The g++ version is g++ (Ubuntu 4.4.3-4ubuntu5) 4.4.3 if that matters. Any ideas what's the problem?

Thanks in advance, Thomas

Answer 1

As an alternative to David's solution, you can unconditionally forward the call to a set of overloaded functions:

template <class T> class array;
namespace details {
  template <class T> std::string array_print(array<T> const&);
  std::string array_print(array<double> const&); // Regular function 
  template <class T> std::string array_print(array<array<T> > const&);
}

template <class T> class array : private vector<T> {
public:
    ...
       std::string printToString() { return details::array_print(*this); }
    ...
};

namespace details { /* implementions after class is defined */ }