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  1. #include <type_traits>
  2.  
  3. template<typename U, typename L>
  4.   static auto Update(volatile U &state, const L &lambda) ->
  5.       //typename std::result_of<L(U,U)>::type
  6.       decltype(lambda(*(U*)0,*(U*)0))
  7.   {
  8.     typedef decltype(lambda(*(U*)0,*(U*)0)) ResultType;
  9.     //typedef typename std::result_of<L(U,U)>::type ResultType;
  10.  
  11.     return Update<ResultType,U,L>(state, lambda, (typename std::is_void<ResultType>::type *)0);
  12.   }
  13.  
  14.   // Specialization for lambda that returns type R (not void)
  15.   template<typename R, typename U, typename L>
  16.   static R Update(volatile U &state, const L &lambda, const std::false_type *)
  17.   {
  18.       // Real code does cmpxchg loop
  19.       return state;
  20.   }
  21.  
  22.   template<typename R, typename U, typename L>
  23.   static void Update(volatile U &state, const L &lambda, const std::true_type *)
  24.   {
  25.       // Real code does cmpxchg loop
  26.   }
  27.  
  28. int main()
  29. {
  30.   int x;
  31.   auto shouldBeBool = Update(x,
  32.   [](int oldvalue, int &newvalue)
  33.   {
  34.     newvalue = oldvalue + 1;
  35.     return true;
  36.   });
  37.  
  38.   return (int)std::is_same<bool,decltype(shouldBeBool)>::value;
  39. }
  40.  
Runtime error #stdin #stdout 0s 2848KB
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https://ideone.com/zqlbTx
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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