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 $offset <p>
* An offset to check for.
* </p>
* @return boolean true on success or false on failure.
* </p>
* <p>
* The return value will be casted to boolean if non-boolean was returned.
* @since 5.0.0
*/
public function offsetExists($offset);
/**
* Offset to retrieve
* @link http://php.net/manual/en/arrayaccess.offsetget.php
* @param mixed $offset <p>
* The offset to retrieve.
* </p>
* @return mixed Can return all value types.
* @since 5.0.0
*/
public function offsetGet($offset);
/**
* Offset to set
* @link http://php.net/manual/en/arrayaccess.offsetset.php
* @param mixed $offset <p>
* The offset to assign the value to.
* </p>
* @param mixed $value <p>
* The value to set.
* </p>
* @return void
* @since 5.0.0
*/
public function offsetSet($offset, $value);
/**
* Offset to unset
* @link http://php.net/manual/en/arrayaccess.offsetunset.php
* @param mixed $offset <p>
* The offset to unset.
* </p>
* @return void
* @since 5.0.0
*/
public function offsetUnset($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
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