MQL's OOP notes: Managing resources by object wrappers

One simple use case where OOP can be helpful is related to resource control. A file is a resource of a special kind. It should be allocated (created), used, and finally released (closed).

This problem can be easily solved by OOP. Let us define a class which wraps file handle and takes care about (potentially, all) manipulations with it. To open a file one will create an automatic object of this class, for example inside a function. And when the flow control will leave the context (the function in this case, or other block of code where the file variable is declared), the object destructor will be called automatically and close file handle. It's important to note that the variable should be declared as automatic, not via a dynamically allocated pointer using operator new (because such a stuff must be deleted explicitly by programmer).  

Here is the simple self-explanatory class.

class File
{
  private:
    int file; // file handle
  
  public:
    File(const string name, const int flags, const short delimiter)
    {
      file = FileOpen(name, flags, delimiter);
    }

    File(const string name, const int flags)
    {
      file = FileOpen(name, flags);
    }
    
    bool isOpened() const
    {
      return (file != INVALID_HANDLE);
    }
    
    bool operator!() const
    {
      return !isOpened();
    }
    
    int handle() const
    {
      return file;
    }
    
    virtual ~File()
    {
      if(file != INVALID_HANDLE)
      {
        Print("File is closed automatically"); // this is just a debug log
        FileClose(file);
      }
    }
};

int processFile(const string inputFileName = "abc.csv")
{
  // declare automatic variable of class File
  File f(inputFileName, FILE_READ | FILE_TXT | FILE_SHARE_READ, ',');
  if(!f)
  {
    Alert("Can't read file " + inputFileName);
    return 1;
  }
  
  int handle = f.handle();

  // these are just placeholders for some actual conditions  
  bool requiredCondition1, requiredCondition2;
  
  Print("Processing started...");
  
  if(!requiredCondition1)
  {
    // FileClose(handle) call is not required
    return 2;
  }
  
  string line = FileReadString(handle);

  Print("More in-depth processing...");

  if(!requiredCondition2)
  {
    // FileClose(handle) call is not required
    return 3;
  }
  
  // ...
  
  Print("Processing done");
  
  // FileClose(handle) call is not required

  return 0;
}