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  1. #include <iostream>
  2. #include <string>
  3. #include <stdexcept>
  4.  
  5. //Some made up configuration data for a Foo class.
  6. struct FooConfig
  7. {
  8.     int i;
  9.     double d;
  10. };
  11.  
  12. //Some made up configuration data for a Bar class.
  13. struct BarConfig
  14. {
  15.     int x;
  16.     double y;
  17. };
  18.  
  19. //Configurations can be shared among classes.
  20. struct SharedConfig
  21. {
  22.     std::string text;
  23. };
  24.  
  25. //The actual wrapper.
  26. template <class T>
  27. class StaticConfig
  28. {
  29. public:
  30.  
  31.     StaticConfig()
  32.     {
  33.         if (!mIsInitialised)
  34.         {
  35.             throw std::runtime_error("Tried to construct uninitialised StaticConfig!");
  36.         }
  37.     }
  38.  
  39.     const T*
  40.     operator -> () const
  41.     {
  42.         return &mConfig;
  43.     }
  44.  
  45. private:
  46.  
  47.     friend class ConfigHandler;
  48.  
  49.     StaticConfig(const T& config)
  50.     {
  51.         mConfig = config;
  52.         mIsInitialised = true;
  53.     }
  54.  
  55.     static T mConfig;
  56.     static bool mIsInitialised;
  57. };
  58.  
  59. template <class T>
  60. T StaticConfig<T>::mConfig;
  61. template <class T>
  62. bool StaticConfig<T>::mIsInitialised = false;
  63.  
  64. //ConfigHandler responsible for loading the data.
  65. class ConfigHandler
  66. {
  67. public:
  68.  
  69.     ConfigHandler() :
  70.         mFooConfig(GetFooConfig()),
  71.         mBarConfig(GetBarConfig()),
  72.         mSharedConfig(GetSharedConfig())
  73.     {}
  74.  
  75.     FooConfig
  76.     GetFooConfig()
  77.     {
  78.         FooConfig fooConfig;
  79.         fooConfig.i = 1337;
  80.         fooConfig.d = 123.45;
  81.         return fooConfig;
  82.     }
  83.  
  84.     BarConfig
  85.     GetBarConfig()
  86.     {
  87.         BarConfig barConfig;
  88.         barConfig.x = 69;
  89.         barConfig.y = 987.65;
  90.         return barConfig;
  91.     }
  92.  
  93.     SharedConfig
  94.     GetSharedConfig()
  95.     {
  96.         SharedConfig sharedConfig;
  97.         sharedConfig.text = "This is a std::string!";
  98.         return sharedConfig;
  99.     }
  100.  
  101. private:
  102.  
  103.     StaticConfig<FooConfig> mFooConfig;
  104.     StaticConfig<BarConfig> mBarConfig;
  105.     StaticConfig<SharedConfig> mSharedConfig;
  106. };
  107.  
  108. class Foo
  109. {
  110. public:
  111.  
  112.     void
  113.     Print()
  114.     {
  115.         std::cout << "Foo prints " << mConfig->i << " " << mConfig->d << " "
  116.                   << mSharedConfig->text << '\n';
  117.     }
  118.  
  119. private:
  120.  
  121.     StaticConfig<FooConfig> mConfig;
  122.     StaticConfig<SharedConfig> mSharedConfig;
  123. };
  124.  
  125. class Bar
  126. {
  127. public:
  128.  
  129.     void
  130.     Print()
  131.     {
  132.         std::cout << "Bar prints " << mConfig->x << " " << mConfig->y << " "
  133.                   << mSharedConfig->text << '\n';
  134.     }
  135.  
  136. private:
  137.  
  138.     StaticConfig<BarConfig> mConfig;
  139.     StaticConfig<SharedConfig> mSharedConfig;
  140. };
  141.  
  142. int main()
  143. {
  144.     //If uncommented, this next line throws as it attempts to...
  145.     //...construct a StaticConfig<FooConfig> inside foo before...
  146.     //...ConfigHandler has a chance to initialise things.
  147.     //Foo aFoo;
  148.  
  149.     //ConfigHandler must only briefly exist to load data.
  150.     ConfigHandler();
  151.     Foo foo;
  152.     Bar bar;
  153.  
  154.     foo.Print();
  155.     bar.Print();
  156.  
  157.     return 0;
  158. }
  159.  
Success #stdin #stdout 0s 15240KB
comments (?)
stdin
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Standard input is empty
stdout
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Foo prints 1337 123.45 This is a std::string!
Bar prints 69 987.65 This is a std::string!
https://ideone.com/IefQz8
language:
C++ (gcc 8.3)
created:
5 years ago
visibility:
public

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