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  1.     #include <utility>
  2.     #include <type_traits>
  3.     #include <cstddef>
  4.  
  5.     template< typename FuncSig, FuncSig func >
  6.     struct Functor {
  7.       template<typename... Args>
  8.       auto operator()(Args&&... args) const
  9.       -> decltype( func(std::forward<Args>(args)...) )
  10.         { return ( func(std::forward<Args>(args)...) ); }
  11.     };
  12.  
  13.     struct Zeroer {
  14.       template<typename T>
  15.       void operator()( T& t ) const {
  16.         t = 0;
  17.       }
  18.     };
  19.     template< typename T, typename Creator, typename Destroyer, typename Nuller=Zeroer >
  20.     struct RAII_handle {
  21.       RAII_handle( std::nullptr_t ):
  22.         data()
  23.       {
  24.         Nuller()(data);
  25.       }
  26.       RAII_handle( RAII_handle const& ) = delete;
  27.       RAII_handle( RAII_handle && o ):data(std::move(o.data)) {
  28.         Nuller()(o.data);
  29.       }
  30.       RAII_handle& operator=( RAII_handle const& ) = delete;
  31.       RAII_handle& operator=( RAII_handle && o ) {
  32.         data = std::move(o.data);
  33.         Nuller()(o.data);
  34.         return *this;
  35.       }
  36.       template<typename... Args>
  37.       RAII_handle( Args&&... args ):
  38.         data( Creator()(std::forward<Args>(args)...) )
  39.       {}
  40.       auto close()->decltype( Destroyer()(std::declval<T&>()) ) {
  41.         auto retval = Destroyer()(data);
  42.         Nuller()(data);
  43.         return retval;
  44.       }
  45.       ~RAII_handle() {
  46.         close();
  47.       }
  48.       T& get() { return data; }
  49.       T const& get() const { return data; }
  50.  
  51.       T& operator*() { return get(); }
  52.       T const& operator*() const { return get(); }
  53.  
  54.       T* operator->() { return &get(); }
  55.       T const* operator->() const { return &get(); }
  56.     private:
  57.       T data;
  58.     };
  59.  
  60.     #include <iostream>
  61.     typedef unsigned char HANDLE;
  62.     HANDLE CreateFile( char const* name ) {
  63.       std::cout << name << "\n";
  64.       return 7;
  65.     }
  66.     bool CloseFile( HANDLE h ) {
  67.       if (h) {
  68.         --h;
  69.         std::cout << (int)h << "\n";
  70.         return true;
  71.       } else {
  72.         std::cout << "already closed\n";
  73.         return false;
  74.       }
  75.     }
  76.  
  77.     typedef RAII_handle< HANDLE, Functor< HANDLE(*)( char const* ), CreateFile >, Functor< bool(*)(HANDLE), CloseFile > > FileHandle;
  78.  
  79.     int main() {
  80.       FileHandle bob("hello.txt");
  81.       unsigned char value = *bob;
  82.       bob.close();
  83.     }
Success #stdin #stdout 0s 2896KB
comments (?)
stdin 
Standard input is empty
stdout 
hello.txt
6
already closed
https://ideone.com/neAQqd
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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