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  1. #include <vector>
  2. #include <utility>
  3. #include <iostream>
  4.  
  5. template <typename T>
  6. class Matrix {
  7.  
  8. private:
  9.  
  10.     class Row {
  11.         friend class Matrix;
  12.  
  13.     public:
  14.         T& operator[] (int j)&&
  15.         {
  16.             return matrix.mappedVector[i * matrix.n + j];
  17.         }
  18.         const T& operator[] (int j) const&&
  19.         {
  20.             return matrix.mappedVector[i * matrix.n + j];
  21.         }
  22.     private:
  23.         int i;
  24.         Matrix& matrix;
  25.  
  26.         Row(int i, Matrix& matrix) :  i(i),   matrix(matrix) {
  27.             std::cout << "int ctor" << std::endl;
  28.         }
  29.  
  30.         Row() {
  31.             std::cout << "ctor" << std::endl;
  32.         }
  33.  
  34.     };
  35. public:
  36.     Matrix() :
  37.         m(0),
  38.         n(0)
  39.     {}
  40.     explicit Matrix(size_t m, size_t n) :   m(m),   n(n),   mappedVector(m* n){
  41.     }
  42.  
  43.  
  44.     Row operator[] (int i) {
  45.         return Row(i, *this);
  46.     }
  47.  
  48.     const Row operator[] (int i) const  {
  49.         return Row(i, *this);
  50.     }
  51.  
  52. private:
  53.     size_t m;
  54.     size_t n;
  55.     std::vector<T> mappedVector;
  56. };
  57.  
  58. int main()
  59. {
  60.     Matrix<int> matrix(2, 5);
  61.     matrix[1][0] = 1;
  62.  
  63.     auto autoRowProxy = matrix[1];
  64.  
  65.     return 0;
  66. }
Success #stdin #stdout 0s 4396KB
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int ctor
int ctor
https://ideone.com/VdkzPq
language:
C++14 (gcc 8.3)
created:
4 years ago
visibility:
secret

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