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  1. #include <iostream>
  2.  
  3. struct mutex {
  4.     void acquire() { std::cout << "Mutex acquired.\n"; }
  5.     void release() { std::cout << "Mutex released.\n"; }
  6. };
  7.  
  8. template <typename T>
  9. struct locker_box {
  10.     struct cookie {
  11.         cookie() : b(nullptr) {}
  12.         cookie(locker_box& b) : b(&b) {}
  13.  
  14.         T& operator*() {
  15.             return b->t;
  16.         }
  17.         T* operator->() {
  18.             return b->t;
  19.         }
  20.         cookie& operator++() {
  21.             b = nullptr;
  22.             return *this;
  23.         }
  24.         cookie operator++(int) {
  25.             cookie copy(*this);
  26.             operator++();
  27.             return copy;
  28.         }
  29.         bool operator==(cookie const& c) {
  30.             return b == c.b;
  31.         }
  32.         bool operator!=(cookie const& c) {
  33.             return b != c.b;
  34.         }
  35.     private:
  36.         locker_box* b;
  37.     };
  38.     struct open_box {
  39.         open_box(locker_box& b) : b(b) { b.m.acquire(); }
  40.         ~open_box() { b.m.release(); }
  41.         cookie begin() { return cookie(b); }
  42.         cookie end() { return cookie(); }
  43.     private:
  44.         locker_box& b;
  45.     };
  46.  
  47.     open_box open() {
  48.         return open_box(*this);
  49.     }
  50.  
  51. private:
  52.     friend class open_box;
  53.     friend class cookie;
  54.     mutex m;
  55.     T t;
  56. };
  57.  
  58. struct not_suitable_for_this_audience {};
  59.  
  60. struct racy {
  61.     void do_racy_stuff() { std::cout << "Being racy...\n"; }
  62.     void do_more_racy_stuff() { std::cout << "Being even more racy...\n"; }
  63.     void do_really_raunchy_stuff() { throw not_suitable_for_this_audience(); }
  64. };
  65.  
  66. int main() {
  67.     locker_box<racy> box;
  68.     try {
  69.         for(auto& x : box.open()) {
  70.             x.do_racy_stuff();
  71.             x.do_more_racy_stuff();
  72.             x.do_really_raunchy_stuff();
  73.         }
  74.     } catch(not_suitable_for_this_audience const&) {
  75.         std::cout << "Ooops..."
  76.     }
  77. }
  78.  
  79. // This prints:
  80. // Mutex acquired.
  81. // Being racy...
  82. // Being even more racy...
  83. // Mutex released.
  84. // Ooops...
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https://ideone.com/QAXNf
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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