在观看Symfony源码的时候，发现了这种写法$this['logger'] = $value $this 是个对象。纳尼，对象也能这么玩，然后我赶紧就试了一下，然后，显而易见，挂掉了。原来，之所以能够当作数组来用是因为，实现了PHP的一个叫做ArrayAccess 接口，随手写了一个示例。 接口说明：：提供像访问数组一样访问对象的能力的接口。

    1. <?php
    2. class base implements ArrayAccess {
    3.     protected $values;
    4.     protected $keys;
    6.     /**
    7.      * Whether a offset exists
    8.      * @link http://php.net/manual/en/arrayaccess.offsetexists.php
    9.      * @param mixed $offset <p>
    10.      * An offset to check for.
    11.      * </p>
    12.      * @return boolean true on success or false on failure.
    13.      * </p>
    14.      * <p>
    15.      * The return value will be casted to boolean if non-boolean was returned.
    16.      * @since 5.0.0
    17.      */
    18.     public function offsetExists($offset){
    19.         return isset($this->keys[$offset]);
    20.     }
    22.     /**
    23.      * Offset to retrieve
    24.      * @link http://php.net/manual/en/arrayaccess.offsetget.php
    25.      * @param mixed $offset <p>
    26.      * The offset to retrieve.
    27.      * </p>
    28.      * @return mixed Can return all value types.
    29.      * @since 5.0.0
    30.      */
    31.     public function offsetGet($offset){
    32.         return $this->values[$offset];
    33.     }
    35.     /**
    36.      * Offset to set
    37.      * @link http://php.net/manual/en/arrayaccess.offsetset.php
    38.      * @param mixed $offset <p>
    39.      * The offset to assign the value to.
    40.      * </p>
    41.      * @param mixed $value <p>
    42.      * The value to set.
    43.      * </p>
    44.      * @return void
    45.      * @since 5.0.0
    46.      */
    47.     public function offsetSet($offset, $value){
    48.         $this->values[$offset] = $value;
    49.     }
    51.     /**
    52.      * Offset to unset
    53.      * @link http://php.net/manual/en/arrayaccess.offsetunset.php
    54.      * @param mixed $offset <p>
    55.      * The offset to unset.
    56.      * </p>
    57.      * @return void
    58.      * @since 5.0.0
    59.      */
    60.     public function offsetUnset($offset){
    61.         unset($this->values[$offset]);
    62.     }
    63. }
    65. class im extends base{
    66.     public function addAttr($key, $value){
    67.         $this[$key] = $value;
    68.         $this->keys[] =$key;
    69.     }
    71.     public function showAttr(){
    72.         return array_combine($this->keys, $this->values);
    73.     }
    74. }
    75. echo '
    76. <pre>';
    77. $im = new im();
    79. $im->addAttr('name', 'zhangsan');
    80. $im->addAttr('addr', 'Shanghai');
    81. $res = $im->showAttr();
    82. echo $im['name'];
    83. var_dump($im);