Be careful of thinking of iterators and arrays as completely analogous in your PHP code. iterator_count will NOT return your iterator to its previous state after looping through it for the count. Any iterator implementation that also implements Countable::count isn't required to do so either.
This is clearest in example form:
$array = array(
1 => 'foo',
2 => 'bar'
foreach ($array as $key => $value)
echo "$key: $value (", count($array), ")\n";
$iterator = new ArrayIterator($array);
foreach ($iterator as $key => $value)
echo "$key: $value (", iterator_count($iterator), ")\n";
1: foo (2)
2: bar (2)
1: foo (2)
Notice that because of how iterator_count works we never see the second iterator value because the next call to then Iterator::valid() implementation returns false (its at the end of the iterator).
(PHP 5 >= 5.1.0)
iterator_count — Count the elements in an iterator
Count the elements in an iterator.
The iterator being counted.
The number of elements in
Example #1 iterator_count() example
$iterator = new ArrayIterator(array('recipe'=>'pancakes', 'egg', 'milk', 'flour'));
The above example will output:
Yes, but ...
Traversable: "Abstract base interface that cannot be implemented alone. Instead it must be implemented by either IteratorAggregate or Iterator."
So You have to implement IteratorAggregate or Iterator because You can not implement Traversable.
Note that you that the iterator parameter doesn't need to be of type Aggregate. As the spl documentation on http://www.php.net/~helly/php/ext/spl/ defines it in the following way:
iterator_count (Traversable $it).
So you can count the number of files in a given directory quite easily:
<?php iterator_count(new DirectoryIterator('path/to/dir/')); ?>