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  1. // helper
  2. template<unsigned N>
  3. struct priority : priority<N-1>{};
  4. template<> struct priority<0>{};
  5.  
  6. // []foo would result in:
  7.  
  8. struct __unnamed__{
  9.   template<class... Ts>
  10.   auto operator()(Ts&&... vs)
  11.       -> decltype(call(priority<5>{}, std::forward<Ts>(vs)...))
  12.   {
  13.     return call(priority<5>{}, std::forward<Ts>(vs)...);
  14.   }
  15.  
  16. private:
  17.   template<class C, class... Ts>
  18.   auto call(priority<5>, C&& o, Ts&&... vs)
  19.       -> decltype(std::forward<C>(o).foo(std::forward<Ts>(vs)...))
  20.   {
  21.     return std::forward<C>(o).foo(std::forward<Ts>(vs)...);
  22.   }
  23.  
  24.   template<class C, class... Ts>
  25.   auto call(priority<4>, C&& o, Ts&&... vs)
  26.       -> decltype(std::forward<C>(o)->foo(std::forward<Ts>(vs)...))
  27.   {
  28.     return std::forward<C>(o)->foo(std::forward<Ts>(vs)...);
  29.   }
  30.  
  31.   template<class C>
  32.   auto call(priority<3>, C&& o)
  33.       -> decltype(std::forward<C>(o).foo)
  34.   {
  35.     return std::forward<C>(o).foo;
  36.   }
  37.  
  38.   template<class C>
  39.   auto call(priority<2>, C&& o)
  40.       -> decltype(std::forward<C>(o)->foo)
  41.   {
  42.     return std::forward<C>(o)->foo;
  43.   }
  44.  
  45.   template<class... Ts>
  46.   auto call(priority<1>, Ts&&... vs)
  47.       -> decltype(foo(std::forward<Ts>(vs)...))
  48.   {
  49.     return foo(std::forward<Ts>(vs)...);
  50.   }
  51. };
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https://ideone.com/OAHh5e
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
secret

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