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  1. // Generic, type-safe delegates.
  2. // (updated from blog.molecular-matters)
  3.  
  4. #include <iostream>
  5.  
  6. template<typename>
  7. struct Delegate {};
  8.  
  9. template<typename R, typename... Args>
  10. struct Delegate<R(Args...)>
  11. {
  12.     Delegate()
  13.     : m_stub{nullptr, nullptr}
  14.     {}
  15.  
  16.     template<R (*Function)(Args...)>
  17.     void bind(void)
  18.     {
  19.         m_stub = {nullptr, s_function_stub<Function>};
  20.     }
  21.  
  22.     template<typename T, R (T::*Function)(Args...)>
  23.     void bind(T* instance)
  24.     {
  25.         m_stub = {instance, s_classmethod_stub<T, Function>};
  26.     }
  27.  
  28.     R invoke(Args&&... args) const
  29.     {
  30.         if (!m_stub.second)
  31.             throw std::runtime_error("Cannot invoke unbound delegate.");
  32.         return m_stub.second(m_stub.first, std::forward<Args>(args)...);
  33.     }
  34.  
  35. private:
  36.     std::pair<void*, R (*)(void*, Args&&...)> m_stub;
  37.  
  38.     template<R (*Function)(Args...)>
  39.     static R s_function_stub(void*, Args&&... args)
  40.     {
  41.         return (Function)(std::forward<Args>(args)...);
  42.     }
  43.  
  44.     template<typename T, R (T::*Function)(Args...)>
  45.     static R s_classmethod_stub(void* instance, Args&&... args)
  46.     {
  47.         return (static_cast<T*>(instance)->*Function)(std::forward<Args>(args)...);
  48.     }
  49. };
  50.  
  51. // Main.
  52.  
  53. void function()
  54. {
  55.     std::cout << __PRETTY_FUNCTION__ << "\n";
  56. }
  57.  
  58. struct Class
  59. {
  60.     bool classmethod(int i, double x)
  61.     {
  62.         std::cout << __PRETTY_FUNCTION__ << " -> ";
  63.         std::cout << i << ", " << x << "\n";
  64.         return true;
  65.     }
  66. };
  67.  
  68. int main()
  69. {
  70.     Delegate<void()> a;
  71.     a.bind<function>();
  72.     a.invoke();
  73.     Class instance;
  74.     Delegate<bool(int, double)> b;
  75.     b.bind<Class, &Class::classmethod>(&instance);
  76.     if (b.invoke(1, 2.3))
  77.         std::cout << "true";
  78. }
Success #stdin #stdout 0s 5316KB
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void function()
bool Class::classmethod(int, double) -> 1, 2.3
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https://ideone.com/SaTwD7
language:
C++ (gcc 8.3)
created:
4 days ago
visibility:
public

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