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  1. template <typename T>
  2. class smart_ptr
  3. {
  4. public:
  5.     // ... removed other member functions for simplicity
  6.     T* get() { return ptr; }
  7.  
  8.     template <typename U>
  9.     auto operator [](U u) const -> decltype((*get())[u])
  10.     {
  11.         return (*get())[u];
  12.     }
  13.  
  14.     template <typename U>
  15.     auto operator [](U u) -> decltype((*get())[u])
  16.     {
  17.         return (*get())[u];
  18.     }
  19.  
  20. /*
  21.     // These work fine:
  22.  
  23.     template <typename U>
  24.     int operator [](U u)
  25.     {
  26.         return (*get())[u];
  27.     }
  28.  
  29.     template <typename U>
  30.     int& operator [](U u)
  31.     {
  32.         return (*get())[u];
  33.     }
  34. */
  35. private:
  36.     T* ptr;
  37. };
  38.  
  39. struct Test
  40. {
  41. };
  42.  
  43. struct Test2
  44. {
  45.     int& operator [](int i) { return m_Val; }
  46.     int operator [](int i) const { return m_Val; }
  47.  
  48.     int m_Val;
  49. };
  50.  
  51. int main()
  52. {
  53.     smart_ptr<Test> p1;
  54.     smart_ptr<Test2> p2;
  55.     p2[0] = 1;
  56. }
Compilation error #stdin compilation error #stdout 0s 0KB
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stdin
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Standard input is empty
compilation info 
prog.cpp: In function 'int main()':
prog.cpp:55:9: error: no match for 'operator[]' in 'p2[0]'
stdout
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Standard output is empty
https://ideone.com/VyjJ28
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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