Thread overview  


September 23, 2002 Another template strangeness  

 
The idea of the following sample code is simple. First, we keep track of matrix features (square, diagonal, column, or row) as a type. Second, we want the type to divert minimally in the process of matrix multiplication. Specifically, this code tries to differentiate multiplication of column matrix by row matrix into two cases: 1) when column matrix and row matrix are the same size the result is square matrix, 2) otherwise the result is general (rectangular) matrix. This code compiles cleanly by g++ 2.96 and KAI C++ 4.0. dmc gives numerious errors about multiple nonidentical declarations of operator*. /* matrix4.cpp */ #include <iostream.h> template <class T, int n> class ColMatrix; template <class T, int m> class RowMatrix; template <class T, int n, int m> class Matrix { protected: T v[n][m]; public: template <class TT, int nn, int mm> friend Matrix<TT,nn,mm> operator*(const ColMatrix<TT,nn> &, const RowMatrix<TT,mm> &); }; template <class T, int n> class SquareMatrix: public Matrix<T,n,n> { public: template <class TT, int nn> friend SquareMatrix<TT,nn> operator*(const ColMatrix<TT,nn> &, const RowMatrix<TT,nn> &); }; template <class T, int n> class ColMatrix: public Matrix<T,n,1> { public: template <class TT, int nn, int mm> friend Matrix<TT,nn,mm> operator*(const ColMatrix<TT,nn> &, const RowMatrix<TT,mm> &); template <class TT, int nn> friend SquareMatrix<TT,nn> operator*(const ColMatrix<TT,nn> &, const RowMatrix<TT,nn> &); }; template <class T, int m> class RowMatrix: public Matrix<T,1,m> { public: template <class TT, int nn, int mm> friend Matrix<TT,nn,mm> operator*(const ColMatrix<TT,nn> &, const RowMatrix<TT,mm> &); template <class TT, int nn> friend SquareMatrix<TT,nn> operator*(const ColMatrix<TT,nn> &, const RowMatrix<TT,nn> &); }; template <class TT, int nn, int mm> Matrix<TT,nn,mm> operator*(const ColMatrix<TT,nn> &a, const RowMatrix<TT,mm> &b) { Matrix<TT,nn,mm> r; for (int i = 0; i < nn; ++i) for (int j = 0; j < mm; ++j) r.v[i][j] = a.v[i][0]*b.v[0][j]; return r; } template <class TT, int nn> SquareMatrix<TT,nn> operator*(const ColMatrix<TT,nn> &a, const RowMatrix<TT,nn> &b) { SquareMatrix<TT,nn> r; for (int i = 0; i < nn; ++i) for (int j = 0; j < nn; ++j) r.v[i][j] = a.v[i][0]*b.v[0][j]; return r; } int main() { ColMatrix<int,2> m1; RowMatrix<int,2> m2; m1*m2; // should give SquareMatrix return 0; } 
September 24, 2002 Re: Another template strangeness  

 
Posted in reply to Iliya Peregoudov  The fix is posted now. Walter 
September 24, 2002 Re: Another template strangeness  

 
Posted in reply to Walter  Walter wrote:
> The fix is posted now. Walter
Ok, but if we change main() in the previous example to
int main()
{
ColMatrix<int,2> m1;
RowMatrix<int,2> m2;
RowMatrix<int,3> m3;
m1*m2; // should give SquareMatrix
m1*m3; // should give Matrix
return 0;
}
compiler say:
m1*m3; // should give Matrix
^
matrix4.cpp(66) : Error: need explicit cast for function parameter 1 to get
from: ColMatrix<int ,2>
to : const ColMatrix<int ,3>
It seems that compiler doesn't see operator*() that return rectangular matrix. [Why does it want to cast the first operator*() argument? The second one should be the choice of the very same priority...]

September 24, 2002 Re: Another template strangeness  

 
Posted in reply to Iliya Peregoudov  Just a thank you to Iliya for exploring these matters, and Walter for fixing them! Hey Walter be sure to put even the most minor patches on c++announce...I check it all the time...I'd like to know what goes on between X.YY.ZZ.01 and X.YY.ZZ.02. Mark 
September 25, 2002 Re: Another template strangeness  

 
Posted in reply to Iliya Peregoudov  >matrix4.cpp(66) : Error: need explicit cast for function parameter 1 to get
>from: ColMatrix<int ,2>
>to : const ColMatrix<int ,3>
The fix for that is posted now too <g>.

September 25, 2002 Re: Another template strangeness  

 
Posted in reply to Mark Evans  "Mark Evans" <Mark_member@pathlink.com> wrote in message news:amqq01$u2i$1@digitaldaemon.com... > Just a thank you to Iliya for exploring these matters, and Walter for fixing > them! Welcs! > Hey Walter be sure to put even the most minor patches on c++announce...I check > it all the time...I'd like to know what goes on between X.YY.ZZ.01 and X.YY.ZZ.02. Done! 
September 25, 2002 Re: Another template strangeness  

 
Posted in reply to Walter  > The fix for that is posted now too <g>.
>
It rocks! Excellent work, Walter!
P.S.: I'm really amazed by the how fast all of this was fixed out. Looks more like a magic!

September 25, 2002 Re: Another template strangeness  

 
Posted in reply to Iliya Peregoudov  "Iliya Peregoudov" <iliyap@mail.ru> wrote in message news:3D91F652.3060300@mail.ru... > > The fix for that is posted now too <g>. > It rocks! Excellent work, Walter! > P.S.: I'm really amazed by the how fast all of this was fixed out. > Looks more like a magic! What was wrong was the template partial ordering code was well tested for type arguments, but apparently none of the stlport tests tested it with value arguments. So once I figured out what was going wrong, it wasn't too hard to fix. 
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