废话少说，上代码（talk is easy ,show me the code）:

<?php
/**
 * 通过 PHP 数组实现的队列
 */
class SimpleQueue
{
    private $_queue = [];
    private $_size = 0;

    public function __construct($size = 10)
    {
        $this->_size = $size;
    }

    // 入队
    public function enqueue($value)
    {
        if (count($this->_queue) > $this->_size) {
            return false;
        }
        array_push($this->_queue, $value);
    }

    // 出队
    public function dequeue()
    {
        if (count($this->_queue) == 0) {
            return false;
        }
        return array_shift($this->_queue);
    }

    public function size()
    {
        return count($this->_queue);
    }
}

$queue = new SimpleQueue(5);
$queue->enqueue(1);
$queue->enqueue(3);
$queue->enqueue(5);
var_dump($queue->dequeue());  # 1
var_dump($queue->size());  # 2