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  1. #include <memory>
  2. #include <string>
  3. #include <map>
  4.  
  5. template <typename> struct manager;
  6.  
  7. template <typename T>
  8. struct managed_resource
  9. {
  10.         typedef std::shared_ptr<manager<T>> manager_ptr;
  11.  
  12.     managed_resource(manager_ptr const & parent)
  13.             : parent_(parent)
  14.         {
  15.         }
  16.  
  17.         /* ... */
  18.  
  19.         manager_ptr parent_;
  20. };
  21.  
  22. template <typename Policy>
  23. struct manager
  24.     : Policy
  25.     , std::enable_shared_from_this<manager<Policy>>
  26. {
  27.         typedef managed_resource<Policy> resource;
  28.         typedef std::shared_ptr<resource> resource_ptr;
  29.  
  30.     resource_ptr get_resource(std::string const & name)
  31.         {
  32.             Policy & p = *this;
  33.             if(p.find(name))
  34.             {
  35.                 return p.get(name);
  36.             }
  37.             resource_ptr res = std::make_shared<resource>(this->shared_from_this());
  38.             p.store(name, res);
  39.             return res;
  40.         }
  41. };
  42.  
  43. struct  map_policy
  44. {
  45.         typedef std::shared_ptr<managed_resource<map_policy>> resource_ptr;
  46.         typedef std::map<std::string, resource_ptr> resources;
  47.  
  48.         bool find(std::string const & name)
  49.         {
  50.             resources::iterator res_it = resources_.find(name);
  51.             return res_it != resources_.end();
  52.         }
  53.  
  54.         resource_ptr get(std::string const & name)
  55.         {
  56.             resources::iterator res_it = resources_.find(name);
  57.             return res_it->second;
  58.         }
  59.  
  60.         void store(std::string const & name, resource_ptr const & res)
  61.         {
  62.             resources_[name] = res;
  63.         }
  64.  
  65.         resources resources_;
  66. };
  67.  
  68. typedef manager<map_policy> my_manager;
  69.  
  70. int main()
  71. {
  72.     auto m = std::make_shared<my_manager>();
  73.     auto res = m->get_resource("test");
  74.     return 0;
  75. }
Success #stdin #stdout 0s 3032KB
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https://ideone.com/F3w2La
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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