c++ テンプレートメタプログラミング 2 行列足し算

 3つの行列を足し算する版できた.

元ネタ
 http://itee.uq.edu.au/~conrad/misc/sanderson_templates_lecture_uqcomp7305.pdf

#include<iostream>

template < typename T1, typename T2 >
class Glue;

class Matrix {
    public:
    int rows;
    int cols;
    double *data;

    Matrix(){}
    Matrix( int in_row, int in_cols ){
        set_size( in_row, in_cols );
    }
    void set_size( int in_rows, int in_cols ){
        data = new double [ in_rows*in_cols ];
        rows = in_rows;
        cols = in_cols;
        for( int i=0; i<rows*cols; i++ ) data[i]=1.0;
    }

    Matrix( const Matrix & X );
    const Matrix operator=( const Matrix& X );

    Matrix( const Glue<Matrix,Matrix> & X );
    const Matrix & operator=( const Glue<Matrix,Matrix> & X );
   
    Matrix( const Glue< Glue<Matrix,Matrix>, Matrix > & X );
    const Matrix & operator=( const Glue< Glue<Matrix,Matrix>, Matrix >  & X );
   
};

template < typename T1, typename T2 >
class Glue {
public:
    const T1 & A;
    const T2 & B;
    Glue( const T1 & in_A, const T2 & in_B ): A(in_A), B(in_B){}
};

Matrix::Matrix( const Glue<Matrix,Matrix> & X ){
    operator=(X);
}

const Matrix & Matrix::operator=( const Glue< Glue<Matrix,Matrix>, Matrix> & X ){
    const Matrix & A = X.A.A;   
    const Matrix & B = X.A.B;   
    const Matrix & C = X.B;   

    set_size( A.rows, A.cols );

    for( int i=0; i<A.rows * A.cols; i++ ){
        data[i] = A.data[i] + B.data[i] + C.data[i];
    }
    return *this;
}

const Matrix & Matrix::operator=( const Glue<Matrix,Matrix> & X ){
    const Matrix & A = X.A;   
    const Matrix & B = X.B;   

    set_size( A.rows, A.cols );

    for( int i=0; i<A.rows * A.cols; i++ ){
        data[i] = A.data[i] + B.data[i];
    }
    return *this;
}

const Glue<Matrix,Matrix> operator+( const Matrix & A, const Matrix & B ){
    return Glue<Matrix, Matrix>(A,B);
}

const Glue< Glue<Matrix,Matrix> ,Matrix> operator+( const Glue<Matrix, Matrix> & P, const Matrix & Q ){
    return Glue< Glue<Matrix,Matrix>, Matrix >(P,Q);
}

int main(){
    Matrix A1(3,4);
    Matrix B1(3,4);
    Matrix C1(3,4);
    Matrix X(3,4);
   
    X = A1 + B1;
    X = A1 + B1 + C1;

    for( int i=0; i<X.rows*X.cols; i++ ) std::cout << X.data[i] << std::endl;

return 0;}