PHP,SPL,ArrayAccess接口

时间:2012-07-04 17:46:28

标签: php arrays spl arrayaccess

我试图了解ArrayAccess Interface背后的想法,

我不明白每个方法的含义,如果那些方法(函数)是“内置”函数而ArrayAccess接口(也是“内置”)只是“确定”我将实现那些“内置”方法(函数)

我试图了解每个函数在我们的代码“幕后花絮”中做了什么。

function offsetSet($offset, $value);
function offsetGet($offset);
function offsetUnset($offset);
function offsetExists($offset);

如果我理解ArrayAccess是一个内置接口,包含要实现的密封,当我们实现它们时,我们只实现对内置函数的引用,如果有人可以帮助我做到这一点,我会很高兴。

2 个答案:

答案 0 :(得分:6)

如果实现该接口,则该对象就像一个数组。例如,如果$foo是实现ArrayAccess的类的实例:

$foo['bar'] = 42来电offsetSet('bar', 42)

echo $foo['bar']来电offsetGet('bar')

unset($foo['bar'])来电offsetUnset('bar')

isset($foo['bar'])来电offsetExists('bar')

你永远不会自己明确地调用函数offset *。当您将对象作为数组访问时,它会隐式发生。

答案 1 :(得分:0)

在比较ArrayAccessSimpleXMLElement(一个没有实现它的内部课程)时,我也很好奇。该接口已在手册中详细记录,因此我想强调一些与偏移类型有关的差异。

但首先是一个实现ArrayAccess的类的样板示例实现,在访问时提供输出:

/**
 * ArrayAccess Example
 */
class ExampleArrayLikeAccess implements ArrayAccess
{

    /**
     * Whether a offset exists
     *
     * @link http://php.net/manual/en/arrayaccess.offsetexists.php
     * @param mixed $offset - An offset to check for.
     * @return boolean true on success or false on failure.
     *
     * The return value will be casted to boolean if non-boolean was returned.
     */
    public function offsetExists($offset) {
        echo "  - offsetExists(", $this->varString($offset),")\n";
    }

    /**
     * Offset to retrieve
     *
     * @link http://php.net/manual/en/arrayaccess.offsetget.php
     * @param mixed $offset The offset to retrieve.
     * @return mixed Can return all value types.
     */
    public function offsetGet($offset) {
        echo "  - offsetGet(", $this->varString($offset),")\n";
    }

    /**
     * Offset to set
     *
     * @link http://php.net/manual/en/arrayaccess.offsetset.php
     * @param mixed $offset The offset to assign the value to.
     * @param mixed $value The value to set.
     * @return void
     */
    public function offsetSet($offset, $value) {
        echo "  - offsetSet(", $this->varString($offset), ", ", $this->varString($value), ")\n";
    }

    /**
     * Offset to unset
     * @link http://php.net/manual/en/arrayaccess.offsetunset.php
     * @param mixed $offset  The offset to unset.
     * @return void
     */
    public function offsetUnset($offset) {
        echo "  - offsetUnset(", $this->varString($offset),")\n";
    }

    /**
     * helper to give a variable dump in form of a string
     */
    private function varString($var) {
        ob_start();
        var_dump($var);
        return trim(strtr(ob_get_clean(), ["\n" => '', "\r" => '']), ' {}');
    }

}

使用它运行一些用法示例。我以评论的形式留下了笔记。它应该是非常自我解释的:

$like = new ExampleArrayLikeAccess();


/* offsetExists */

// indexes/keys that behave similar to PHP arrays:

isset($like[1]);    # integer stay integer
# offsetExists(int(1))

isset($like['1']);  # string like an integer - converted to integer
# offsetExists(int(1))

isset($like['01']); # string unlike an integer - stays string
# offsetExists(string(2) "01")

isset($like[TRUE]); # booleans are converted to integer
# offsetExists(bool(true))

// indexes/keys that differ to PHP arrays:

isset($like[1.1]);     # a float stays a float (double)
# offsetExists(double(1.1))

isset($like[NULL]);    # NULL stays NULL
# offsetExists(NULL)

isset($like[array()]); # array stays array
# offsetExists(array(0))

isset($like[$like]);   # object stays object
# offsetExists(class SxeLikeAccess#2 (0))


/* offsetGet */

// indexes/keys behave the same as with offsetExists:
$like[1];    # offsetGet(int(1))
$like['1'];  # offsetGet(int(1))
$like['01']; # offsetGet(string(2) "01")
// ...


/* offsetSet */

$like[1] = 'value';    # index/key behaves the same as with offsetExists
# offsetSet(int(1), string(5) "value")

$like[] = 'value';     # index/key is NULL
# offsetSet(NULL, string(5) "value")

$like[NULL] = 'value'; # index/key is NULL
# offsetSet(NULL, string(5) "value")


/* offsetUnset */
unset($like[1]);       # index/key behaves the same as with offsetExists
unset($like[NULL]);    # same for NULL

与标准PHP数组的主要区别在于,您不仅可以使用整数和字符串作为偏移量。