问PHP中的迭代变量是什么?我们为什么要使用它？

EN

<?php
    class myIterator implements Iterator {
        private $position = 0;
        private $array = array("A","B","C",);

        public function __construct() {
            $this->position = 0;
        }
        function rewind() {
            $this->position = 0;
        }
        function current() {
            return $this->array[$this->position];
        }
        function key() {
            return $this->position;
        }
        function next() {
            $this->position++;
        }
        function valid() {
            return isset($this->array[$this->position]);
        }
    }

    $it = new myIterator;

    foreach($it as $key => $value) {
        var_dump($key, $value);
        echo "\n";
    }

<?php
    class myIterable {
        function foo(iterable $iterable){
            foreach ($iterable as $key => $value) {
                var_dump($key, $value);
                echo "\n";
            }
        }
    }
    $it = new myIterable;
    $it->foo(array("A","B","C",));