decorator/composition with iterators

[Warboss_Alex]

There is probably a very simple solution to this but I can't seem to find it.

How can you decorate an iterator with another iterator? For example:

$iterator = new OriginalIterator($result);
$decoratorIterator = new DecoratorIterator($iterator);
foreach ($decoratorIterator as $item) {
 //do something
} 

What exactly do I need to put into my DecoratorIterator::current() method? I know if DecoratorIterator inherited from OriginalIterator I would just put in a call to parent::current() and then do something with the data but I'm trying to avoid inheritance here so I can pass the OriginalIterator around - or is this the wrong way to do it?

Any help is appreciated!

[oddz]

OrigionalIterator and DecoratorInterator should share the same interface.

interface MyAbtractIterator {

    public function next();
    public function hasNext();
    public function reset();
    
} 

OrigionalIterator implements MyAbtractIterator {

    public function __construct($result) { ... }
    
    public function next() { ... }
    
    public function hasNext() { ... }
    
    public function reset() { ... }

} 

DecoratorIterator implements MyAbtractIterator {

    protected $iterator;

    public function __construct(MyAbtractIterator $iterator) {
    
        $this->iterator = $iterator;
    
    }
    
    public function next() {

                 // change behavior here
    
        return $this->iterator->next();
    
    }
    
    public function hasNext() {

               // change behavior here
    
        return $this->iterator->hasNext();
    
    }
    
    public function reset() {

               // change behavior here
    
        return $this->iterator->reset();
    
    }

} 

[Ren]

SPL has an OuterIterator interface *, meant for such cases, which implement for decorating iterators...

<?php

    class DecoratingIterator implements OuterIterator
    {
        protected $inner;

        function __construct(Iterator $inner) { $this->inner = $inner; }
        function next() { $this->inner->next(); }
        function rewind() { $this->inner->rewind(); }
        function key() { return $this->inner->key(); }
        function current() { return $this->inner->current(); }
        function valid() { return $this->inner->valid(); }

        function getInnerIterator() { return $this->inner; }
    }

    class SquaringIterator extends DecoratingIterator
    {
        function current()
        {
            $r = parent::current();
            return $r * $r;
        }
    }

    $di = new SquaringIterator(new ArrayIterator(array(0, 1, 2)));

    foreach($di as $v)
        echo $v, "\n";

* this should've been a class, imo, would save having to create a class.

[Warboss_Alex]

thanks guys!

[Peter Goodman]

Also see the SPL's IteratorIterator, it implements the boilerplate that you would otherwise need to do manually. Also note that in some cases it acts strangely.

[Warboss_Alex]

Also see the SPL's IteratorIterator, it implements the boilerplate that you would otherwise need to do manually. Also note that in some cases it acts strangely.

Ah, I knew I'd heard about that somewhere! Thanks to everyone!