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  1. #include <type_traits>
  2. #include <utility>
  3. #include <iostream>
  4. #include <vector>
  5.  
  6. template <typename Type>
  7. class ptr_scope_manager
  8. {
  9. private:
  10.     std::vector<Type> ptrs;
  11.  
  12. public:
  13.     template <typename T = Type, typename... Args>
  14.     auto create(Args&&... args) -> typename std::enable_if<!std::is_constructible<T, Args...>::value, T*>::type
  15.     {
  16.     	std::cout << "push_back" << std::endl;
  17.         ptrs.push_back(T{ std::forward<Args>(args)... });
  18.         return &ptrs.back();
  19.     }
  20.  
  21.     template <typename T = Type, typename... Args>
  22.     auto create(Args&&... args) -> typename std::enable_if<std::is_constructible<T, Args...>::value, T*>::type
  23.     {
  24.     	std::cout << "emplace_back" << std::endl;
  25.         ptrs.emplace_back(std::forward<Args>(args)...);
  26.         return &ptrs.back();
  27.     }
  28. };
  29.  
  30. class public_ctor
  31. {
  32.     int i;
  33.  
  34. public:
  35.     public_ctor(int i): i(i) {} // public
  36. };
  37.  
  38. class private_ctor
  39. {
  40.     friend class ptr_scope_manager<private_ctor>;
  41.     int i;
  42.  
  43. private:
  44.     private_ctor(int i): i(i) {} // private
  45. };
  46.  
  47. class non_friendly_private_ctor
  48. {    int i;
  49.  
  50. private:
  51.     non_friendly_private_ctor(int i): i(i) {} // private
  52. };
  53.  
  54.  
  55. int main()
  56. {
  57.     ptr_scope_manager<public_ctor> public_manager;
  58.     ptr_scope_manager<private_ctor> private_manager;
  59.     ptr_scope_manager<non_friendly_private_ctor> non_friendly_private_manager;
  60.  
  61.     public_manager.create(3);
  62.  
  63.     private_manager.create(3);
  64.  
  65.     // non_friendly_private_manager.create(3); raises error
  66. }
  67.  
Success #stdin #stdout 0s 3428KB
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Standard input is empty
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emplace_back
push_back
https://ideone.com/jzkBc2
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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