single.cpp

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#include <iostream>
#include <ostream>
template <char i> class Index
{
public:
  Index(){};
};
 
class Tensor1;
 
template <class A, char i> class Tensor1_Expr
{
  A *iter;
 
public:
  Tensor1_Expr(A *a) : iter(a) {}
  double &operator()(const int N) { return (*iter)(N); }
  double operator()(const int N) const { return (*iter)(N); }
 
  const A operator=(const Tensor1_Expr<Tensor1, 'i'> &result)
  {
    cout << "equaling" << endl;
    iter->data0 = result(0);
    iter->data1 = result(1);
    iter->data2 = result(2);
    return *iter;
  }
 
  //    template<class B>
  //    const A operator=(const Tensor1_Expr<B,'i'> &result)
  //    {
  //      cout << "equaling" << endl;
  //      iter->data0=result(0);
  //      iter->data1=result(1);
  //      iter->data2=result(2);
  //      return iter;
  //    }
};
 
class Tensor1
{
public:
  double data0, data1, data2;
 
public:
  Tensor1(double d0, double d1, double d2) : data0(d0), data1(d1), data2(d2) {}
  double &operator()(const int N)
  {
    return N == 0 ? data0 : (N == 1 ? data1 : data2);
  }
 
  double operator()(const int N) const
  {
    return N == 0 ? data0 : (N == 1 ? data1 : data2);
  }
 
  template <char i> Tensor1_Expr<Tensor1, i> operator()(const Index<i> index)
  {
    return Tensor1_Expr<Tensor1, i>(this);
  }
 
  friend ostream &operator<<(ostream &s, const Tensor1 &a);
};
 
ostream &operator<<(ostream &s, const Tensor1 &a)
{
  return s << a.data0 << " " << a.data1 << " " << a.data2 << " ";
}
 
int main()
{
  Tensor1 y(0, 1, 2);
  Tensor1 x(2, 3, 4);
  const Index<'i'> i;
 
  y(i) = x(i);
 
  cout << y << endl;
}