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  1. #include <type_traits>
  2. #include <memory>
  3. #include <iostream>
  4.  
  5. template <typename L, typename R, typename... Args>
  6. struct LambdaWrapper {
  7.     static void set(const L& lambda) { m_l.reset(new L(lambda)); }
  8.     static R callback(Args&& ... args) { return (*m_l)(std::forward<Args>(args)...); }
  9.  
  10. private:
  11.     static std::unique_ptr<L> m_l;
  12. };
  13.  
  14. template <typename L, typename R, typename... Args>
  15. std::unique_ptr<L> LambdaWrapper<L, R, Args...>::m_l;
  16.  
  17. template <typename L, typename R, typename... Args>
  18. auto mem_func_to_wrapper(R (L::*)(Args...))
  19.   -> LambdaWrapper<L, R, Args...>; // undefined!
  20.  
  21. template <typename L, typename R, typename... Args>
  22. auto mem_func_to_wrapper(R (L::*)(Args...) const)
  23.   -> LambdaWrapper<L, R, Args...>; // undefined!
  24.  
  25. template <typename L>
  26. auto lambda_to_wrapper(const L&)
  27.   -> decltype(mem_func_to_wrapper(&L::operator())); // undefined!
  28.  
  29. int main() {
  30.     std::size_t toBeCaptured = 100;
  31.     auto lambda =
  32.     [&](std::string& str) -> std::size_t {
  33.         return toBeCaptured + str.length();
  34.     };
  35.     typedef decltype(lambda_to_wrapper(lambda)) CallbackSupportType;
  36.     CallbackSupportType::set(lambda);
  37.     std::size_t (*pFunc)(std::string&) = &CallbackSupportType::callback;
  38.     std::string str("may work?");
  39.     std::size_t ret = pFunc(str);
  40.     std::cout << "Result: " << ret << std::endl;
  41. }
Success #stdin #stdout 0s 3016KB
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Standard input is empty
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Result: 109
https://ideone.com/ROiFwi
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
secret

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