Using the Memento Pattern with a File Reading Class - Defining the signature of a caretaker class
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As you might have guessed, the functionality of a caretaker class has to be strongly related to the nature of the tasks performed by the originator. Keeping in mind this basic principle, below I listed the definition for the corresponding caretaker. In a fit of inspiration, I named it "FileDataSeeker." Take a look at it, please:
// define 'FileDataSeeker' class (in this case, this is the
Caretaker class)
class FileDataSeeker{
private $filePointer;
// the constructor takes up the originator object as the only
input parameter
public function __construct(FileDataReader $fileDataReader){
$this->setFilePointer($fileDataReader);
}
public function setFilePointer(FileDataReader $fileDataReader){
$this->filePointer=$fileDataReader->getFilePointer();
}
public function getFilePointer(FileDataReader $fileDataReader){
$fileDataReader->setFilePointer($this->filePointer);
}
}
As illustrated above, the "FileDataSeeker" class has some useful methods for handling the "filePointer" property that belongs to the respective originator class. These methods will help this caretaker class to carry out its responsibility to store the value of the property. Thus, the value can be retrieved at a later time. Pretty logical, isn't it?
By providing the "FileDataSeeker" class with this ability, if the file reading class locates its file pointer at a non-existent place, it will be possible to move it back to a valid position via the respective caretaker. Definitely, that makes a lot of sense!
However, showing you the originator and the caretaker separately won't give you a clear idea of how they work. Thus, in response to this issue, in the next section I'll create a simple script, which hopefully will demonstrate the power of these two classes when they operate together.
As usual, to see how this will be achieved, go ahead and read the following section. I'll be there, waiting for you.
Next: The memento design pattern in action >>
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