ceph/src/boost/libs/move/example/doc_file_descriptor.cpp

   1 //////////////////////////////////////////////////////////////////////////////
   2 //
   3 // (C) Copyright Ion Gaztanaga 2008-2012.
   4 // Distributed under the Boost Software License, Version 1.0.
   5 // (See accompanying file LICENSE_1_0.txt or copy at
   6 // http://www.boost.org/LICENSE_1_0.txt)
   7 //
   8 // See http://www.boost.org/libs/move for documentation.
   9 //
  10 //////////////////////////////////////////////////////////////////////////////
  11
  12 //[file_descriptor_def
  13
  14 #include <boost/move/utility_core.hpp>
  15 #include <stdexcept>
  16
  17 class file_descriptor
  18 {
  19    //<-
  20    int operating_system_open_file(const char *)
  21    {
  22       return 1;
  23    }
  24
  25    void operating_system_close_file(int)
  26    {}
  27    //->
  28    int os_descr_;
  29
  30    private:
  31    BOOST_MOVABLE_BUT_NOT_COPYABLE(file_descriptor)
  32
  33    public:
  34    explicit file_descriptor(const char *filename)              //Constructor
  35       : os_descr_(operating_system_open_file(filename))
  36    {
  37       //=if(!os_descr_)
  38          //=throw std::runtime_error("file not found");
  39    }
  40
  41    ~file_descriptor()                                          //Destructor
  42    {  if(os_descr_)  operating_system_close_file(os_descr_);  }
  43
  44    file_descriptor(BOOST_RV_REF(file_descriptor) x)            // Move ctor
  45       :  os_descr_(x.os_descr_)
  46    {  x.os_descr_ = 0;  }
  47
  48    file_descriptor& operator=(BOOST_RV_REF(file_descriptor) x) // Move assign
  49    {
  50       if(os_descr_) operating_system_close_file(os_descr_);
  51       os_descr_   = x.os_descr_;
  52       x.os_descr_ = 0;
  53       return *this;
  54    }
  55
  56    bool empty() const   {  return os_descr_ == 0;  }
  57 };
  58
  59 //]
  60
  61 //[file_descriptor_example
  62 #include <boost/container/vector.hpp>
  63 #include <cassert>
  64
  65 //Remember: 'file_descriptor' is NOT copyable, but it
  66 //can be returned from functions thanks to move semantics
  67 file_descriptor create_file_descriptor(const char *filename)
  68 {  return file_descriptor(filename);  }
  69
  70 int main()
  71 {
  72    //Open a file obtaining its descriptor, the temporary
  73    //returned from 'create_file_descriptor' is moved to 'fd'.
  74    file_descriptor fd = create_file_descriptor("filename");
  75    assert(!fd.empty());
  76
  77    //Now move fd into a vector
  78    boost::container::vector<file_descriptor> v;
  79    v.push_back(boost::move(fd));
  80
  81    //Check ownership has been transferred
  82    assert(fd.empty());
  83    assert(!v[0].empty());
  84
  85    //Compilation error if uncommented since file_descriptor is not copyable
  86    //and vector copy construction requires value_type's copy constructor:
  87    //boost::container::vector<file_descriptor> v2(v);
  88    return 0;
  89 }
  90 //]