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  1. #include <new>
  2. #include <type_traits>
  3. #include <utility>
  4.  
  5.     template <typename F>
  6.     struct RAIIFunctor {
  7.       typedef typename std::remove_reference<F>::type functor_type;
  8.  
  9.       typename std::aligned_storage<sizeof(functor_type), 
  10.                 std::alignment_of<functor_type>::value>::type store;
  11.  
  12.       functor_type* f;
  13.  
  14.       RAIIFunctor() : f{nullptr} {}
  15.       ~RAIIFunctor() { destroy(); }
  16.  
  17.       template <class T>
  18.       void assign(T&& t) {
  19.         destroy();
  20.         f = new(&store) functor_type {std::forward<T>(t)};
  21.       }
  22.  
  23.       void destroy() {
  24.         if (f) 
  25.           f->~functor_type();
  26.         f = nullptr;
  27.       }
  28.  
  29.       void operator()() {
  30.         (*f)();
  31.       }
  32.     };
  33.  
  34.  
  35.     template <typename T>
  36.     void assign_lambda(T&& f)
  37.     {
  38.       static RAIIFunctor<T> func;
  39.  
  40.       func.assign(std::forward<T>(f));
  41.       func();
  42.     }
  43.  
  44. #include <iostream>
  45. #include <memory>
  46. struct S {
  47.   int i_;
  48.   S(int i) : i_{i} {}
  49.   ~S() { std::cout << "~S " << i_ << std::endl; }  
  50. };
  51.  
  52. int main() {
  53.   S s(1);
  54.   auto ptr = std::make_shared<S>(2);
  55.   assign_lambda([ptr](){ std::cout << "lambda\n";} );
  56.   std::cout << "end main\n";
  57. }
Success #stdin #stdout 0s 2988KB
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Standard input is empty
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lambda
end main
~S 1
~S 2
https://ideone.com/3N2PVe
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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