Re: Partial Specialization Method

From:

Markus Schoder <a3vr6dsg-usenet@yahoo.de>

Newsgroups:

comp.lang.c++

Date:

06 May 2007 16:56:02 GMT

Message-ID:

<pan.2007.05.06.16.56.02@yahoo.de>

On Sun, 06 May 2007 09:11:10 -0700, MathStuf wrote:

I have a matrix class and I would like to add a method that is only
applicable when the template type is a of another class. How can I
specialize the class to allow for the new method and hide it with any
other type?

template<class T> class Matrix
{
   public:
      Matrix();
      Matrix(Ini
&ini); // Only
applicable with MyClass
      Matrix(unsigned w, unsigned h, T &d = T());

It is illegal to bind a rvalue to a non-const reference. Make this a
const T & if possible.

      void ImportIni(Ini
&ini); // Only applicable
with MyClass
      void ExportIni(std::ofstream &fout, const String &val);// Only
applicable with MyClass

      void AddRow(T &d = T());
      void AddCol(T &d = T());
      bool InsertRow(unsigned pos, T &d = T()); bool InsertCol(unsigned
      pos, T &d = T()); bool DeleteRow(unsigned pos);
      bool DeleteCol(unsigned pos);

      bool Set(unsigned row, unsigned col, T &s);

      T Get(unsigned row, unsigned col);
      std::vector<T> GetRow(unsigned row);
      std::vector<T> GetCol(unsigned col);
      unsigned GetHeight();
      unsigned GetWidth();

      T operator[](Point &p);
      std::vector<T> operator[](int col);
   private:
      std::vector< std::vector<T> > matrix; unsigned height;
      unsigned width;
};

You can do it with template specialization, like so:

template<class T> struct Base
{
  // all common stuff from above
  // ...
};

template<class T> struct Matrix : Base<T>
{
  Matrix();
  Matrix(unsigned w, unsigned h);
};

class MyClass;
class Ini;

template<> struct Matrix<MyClass> : Base<MyClass>
{
  Matrix();
  Matrix(unsigned w, unsigned h);

  // additional stuff
  Matrix(Ini &ini);
  // ...
};

There is some unavoidable duplication for the constructors unfortunately.

--
Markus