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  1. #include <cstddef>
  2. #include <iostream>
  3.  
  4. template<typename Dst,typename Src>
  5. Dst* pointer_cast(Src *ptr){
  6.     return static_cast<Dst*>(static_cast<void*>(ptr));
  7. }
  8. template<typename Dst,typename Src>
  9. Dst* pointer_cast(Src const* ptr){
  10.     return static_cast<Dst*>(static_cast<void const*>(ptr));
  11. }
  12.  
  13. class Vector{
  14. protected:
  15.     char *data;
  16.     std::size_t elem_size;
  17.  
  18.     Vector(std::size_t size) : data(new char[3*size]),elem_size(size){
  19.     }
  20.  
  21.     char *at(std::size_t index){
  22.         return data + elem_size * index;
  23.     }
  24.     char const* at(std::size_t index) const{
  25.         return data + elem_size * index;
  26.     }
  27.  
  28.     void doSomething();
  29. };
  30. void Vector::doSomething(){
  31.     //処理が隠蔽できる
  32. }
  33. template<typename T>
  34. class Vector_ : Vector{
  35. public:
  36.     Vector_() : Vector(sizeof(T)){
  37.     }
  38.  
  39.     T &operator [](std::size_t index){
  40.         return *pointer_cast<T>(this->at(index));
  41.     }
  42.     T const& operator[](std::size_t index) const{
  43.         return *pointer_cast<T const>(this->at(index));
  44.     }
  45. };
  46. template<typename T>
  47. std::ostream& operator <<(std::ostream& os,Vector_<T> const& v){
  48.     return os << '[' << v[0] <<  ',' << v[1] << ',' << v[2] << ']';
  49. }
  50.  
  51. int main(){
  52.     Vector_<int> v;
  53.     v[0] = 1;
  54.     v[1] = 2;
  55.     v[2] = 3;
  56.     std::cout << v << std::endl;
  57.  
  58.     Vector_<double> v2;
  59.     v2[0] = 0.0;
  60.     v2[1] = 3.14;
  61.     v2[2] = 2.71;
  62.     std::cout << v2 << std::endl;
  63.     return 0;
  64. }
  65.  
Success #stdin #stdout 0s 3028KB
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Standard input is empty
stdout
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[1,2,3]
[0,3.14,2.71]
https://ideone.com/l2aW9M
language:
C++ (gcc 8.3)
created:
11 years ago
visibility:
public

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