Question

Let’s say you want to construct an Iterator that spits out File objects. What type of data do you usually provide to the constructor of such an Iterator?

• an array of pre-constructed File objects, or
• simply raw data (multidimensional array for instance), and let the Iterator create File objects on the fly when Iterated through?

Edit:
Although my question was actually ment to be as general a possible, it seems my example is a bit to broad to tackle general, so I’ll elaborate a bit more. The File objects I’m talking about are actually file references from a database. See these two tables:

folder
| id | folderId | name             |
------------------------------------
|  1 |     null | downloads        |

file
| id | folderId | name             |
------------------------------------
|  1 |        1 | instructions.pdf |

They reference actual folders and files on a filesystem.

Now, I created a FileManager object. This will be able to return a listing of folders and files. For instance:

FileManager::listFiles( Folder $folder );

… would return an Iterator of File objects (or, come to think of it, rather FileReference objects) from the database.

So what my question boils down to is:
If the FileManager object constructs the Iterator in listFiles() would you do something like this (pseudo code):

listFiles( Folder $folder )
{
    // let's assume the following returns an multidimensional array of rows
    $filesData = $db->fetch( $sqlForFetchingFilesFromFolder );
    // let the Iterator take care of constructing the FileReference objects with each iteration
    return FileIterator( $filesData );

}

or (pseudo code):

listFiles( Folder $folder )
{
    // let's assume the following returns an multidimensional array of rows
    $filesData = $db->fetch( $sqlForFetchingFilesFromFolder );
    $files = array();
    for each( $filesData as $fileData )
    {
        $files.push ( new FileReference( $fileData ) );
    }
    // provide the Iterator with precomposed FileReference objects
    return FileIterator( $files );

}

Hope this clarifies things a bit.

Answer 1

What is your “File” object meant to be? An open handle to a file, or a representation of a file system path which can be opened in turn?

It would generally be a bad idea to open all the files at once – after all, part of the point of using an iterator is that you only access one object at a time. Your iterator could yield one open file at a time, and let the caller take responsibility for closing it, although again that might be slightly odd to use.

Your requirements aren’t clear, to be honest – in my experience, most iterators which yield a series of files use something like Directory.GetFiles(pattern) – you don’t pass them the raw data at all, you pass them something which they can use to find the data for you.

It’s not obvious what you’re trying to get at – it feels like you’re trying to ask a general question, but you haven’t provided enough information to let us advise you. It’s like asking, “Do I want to use a string or an integer?” without giving any context.

EDIT: I would probably push all of that logic into FileIterator, personally. Otherwise it’s hard to see what value it’s really providing. In a language like C# or Python you wouldn’t need a separate class in the first place – you’d just use a generator of some description. In that sense this question isn’t language agnostic 🙁