Re: Partial Specialization Method

From:
Markus Schoder <a3vr6dsg-usenet@yahoo.de>
Newsgroups:
comp.lang.c++
Date:
06 May 2007 18:03:59 GMT
Message-ID:
<pan.2007.05.06.18.03.57@yahoo.de>
On Sun, 06 May 2007 10:01:57 -0700, MathStuf wrote:

On May 6, 12:56 pm, Markus Schoder <a3vr6dsg-use...@yahoo.de> wrote:

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


Would it just be easier to make methods that throw() for the other types
then?


Yes probably, but I would rather not implement these methods for the
other types at all or even better use a compile time assertion. That way
the linker resp. compiler will tell you if someone tries to use these
methods with the wrong class.

--
Markus

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