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  1. #include <iostream>
  2. #include <utility>
  3. #include <memory>
  4.  
  5. template<class Sig>class func;
  6. namespace details{
  7.   template<class Sig>struct inner;
  8.   template<class R,class...Args>
  9.   struct inner<R(Args...)>{
  10.     virtual ~inner() {};
  11.     virtual R invoke(Args&&...args) =0;
  12.   };
  13.   template<class F,class Sig>struct impl;
  14.   template<class F,class R,class...Args>
  15.   struct impl<F,R(Args...)>:inner<R(Args...)>{
  16.     F f;
  17.     template<class... Ts>
  18.     impl(Ts&&...ts):f(std::forward<Ts>(ts)...){}
  19.     R invoke(Args&&...args)override{
  20.       return f(std::forward<Args>(args)...);
  21.     }
  22.   };
  23. }
  24. template<class T>struct emplace_as{};
  25. template<class R,class...Args>
  26. class func<R(Args...)>{
  27.   std::unique_ptr<details::inner<R(Args...)>> pImpl;
  28. public:
  29.   R operator()(Args...args){
  30.     return pImpl->invoke(std::forward<Args>(args)...);
  31.   }
  32.   explicit operator bool()const{return pImpl;}
  33.   func(func&&)=default;
  34.   template<class F,class...Ts,class=typename std::enable_if<
  35.     std::is_convertible<decltype(std::declval<F>()(std::declval<Args>()...)),R>::value
  36.   >::type>
  37.   func(emplace_as<F>,Ts&&...ts):
  38.     pImpl( new details::impl<F, R(Args...)>{std::forward<Ts>(ts)...} )
  39.   {}
  40.  
  41.   template<class F,class=typename std::enable_if<
  42.     std::is_convertible<decltype(std::declval<F>()(std::declval<Args>()...)),R>::value
  43.   >::type>
  44.   func(F&&f):
  45.     func(
  46.       emplace_as<typename std::decay<F>::type>(),
  47.       std::forward<F>(f)
  48.     )
  49.   {}
  50. };
  51.  
  52. int main() {
  53.     func<void()> test = [](){ std::cout << "hello world\n"; };
  54. 	test();
  55. }
Success #stdin #stdout 0s 3428KB
comments (?)
stdin 
Standard input is empty
stdout 
hello world
https://ideone.com/JNkVGM
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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