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Upgrading to PHP 5 by Adam Trachtenberg

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Implementing the RecursiveIterator Interface

The RecursiveIterator interface extends the existing Iterator interface to include two additional methods: hasChildren( ) and getChildren( ). These methods are used to navigate through sublists.

If you have an existing Iterator, it’s natural to extend it to include the additional methods. SPL actually comes with a RecursiveDirectoryIterator, so there’s no need to add these methods to DirectoryIterator, but it’s a useful exercise to see how these methods should behave.

Here’s how it’s done:

class MyRecursiveDirectoryIterator extends MyDirectoryIterator 
                                   implements RecursiveIterator {

    protected function getPath( ) {
        return $this->path . DIRECTORY_SEPARATOR . $this->current( );
    }

    public function hasChildren( ) {
        return is_dir($this->getPath( ));
    }
    
    public function getChildren( ) {
        return new MyRecursiveDirectoryIterator($this->getPath( ));
    }
}

Wow! This is much shorter than the code that was needed for iterate_dir( ). Since you can inherit methods from your earlier iterator, the implementation is three one-line methods.

The first method, getPath( ), constructs a complete pathname from the original path and the current filename. It uses the $path property that was stored in the constructor for MyDirectoryIterator in Example 6-1 because I knew you’d need it now.

The other two methods required by the interface also turn out to be easy to code. A file has children if it’s a directory, so hasChildren( ) only needs to check the return value of is_dir( ...

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