【PHP高级特性】ArrayAccess 接口

php提供了6个常用的预定义接口,实现某些特定的能力。其中最最常用的就是 ArrayAccess 了,像 Laravel 这种流行的框架都用到了它。

ArrayAccess 是啥

如官方文档所述,它“提供像访问数组一样访问对象的能力的接口”。

它提供了4个接口

/**
 * Interface to provide accessing objects as arrays.
 * @link http://php.net/manual/en/class.arrayaccess.php
 */
interface 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. * @since 5.0.0 */ public function offsetExists($offset); /** * 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. * @since 5.0.0 */ public function offsetGet($offset); /** * 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 * @since 5.0.0 */ public function offsetSet($offset, $value); /** * Offset to unset * @link http://php.net/manual/en/arrayaccess.offsetunset.php * @param mixed $offset

* The offset to unset. *

* @return void * @since 5.0.0 */ public function offsetUnset($offset); }

我们实现这4个接口,依次对应数组的isset,读取,设置,unset操作。

有什么用

定义说的很明白啦,提供像访问数组一样访问对象的能力。用上了它,可以让一个类即可以支持对象引用,也支持数组引用。

代码实现示例

class Container implements ArrayAccess
{

    /**
     * @var array 单例对象索引
     */
    private $instances = [];

    /**
     * @var array 可实例化对象定义索引
     */
    private $definitions = [];

    public function offsetExists($offset)
    {
        return isset($this->definitions[$offset]);
    }

    public function offsetGet($offset)
    {
        if (isset($this->instances[$offset])) {
            return $this->instances[$offset];
        } elseif (isset($this->definitions[$offset])) {
            return $this->make($offset);
        }

        throw new \Exception('未提供对象定义');
    }

    public function offsetSet($offset, $value)
    {
        // ... 省略一些较验判断
        $this->definitions[$offset] = $value;
    }

    public function offsetUnset($offset)
    {
        unset($this->definitions[$offset]);
        unset($this->instances[$offset]);
    }

    private function make($offset)
    {
        $definition = $this->definitions[$offset];

        if ($definition instanceof \Closure) {
            return $this->instances[$offset] = $definition();
        }

        if (is_object($definition)) {
            return $this->instances[$offset] = $definition;
        }

        if (is_array($definition)) {
            $class = $definition['class'];
            $reflection = new \ReflectionClass($class);

            $dependencies = [];
            // ... 省略反射的实现代码
            $object = $reflection->newInstanceArgs($dependencies);
            return $this->instances[$offset] = $object;
        }

        throw new \Exception('对象定义不合法');
    }
}

使用示例

$container = new Container();

$container['test'] = function () {
  return 'this is a test';
};

var_dump(isset($container['test']));

echo $container['test'];

unset($container['test']);

参考

预定义接口

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