ArrayAccess::offsetExists

(PHP 5, PHP 7)

检查一个偏移位置是否存在

说明

abstractpublicArrayAccess::offsetExists(mixed $offset):boolean

检查一个偏移位置是否存在。

对一个实现了ArrayAccess接口的对象使用isset()或empty()时，此方法将执行。

Note:

当使用empty()并且仅当ArrayAccess::offsetExists()返回TRUE时，ArrayAccess::offsetGet()将被调用以检查是为否空。

参数

$offset

需要检查的偏移位置。

返回值

成功时返回TRUE，或者在失败时返回FALSE。

Note:

如果一个非布尔型返回值被返回，将被转换为布尔型。

范例

Example #1 ArrayAccess::offsetExists()范例

<?php
class obj implements arrayaccess {
    public function offsetSet($offset, $value) {
        var_dump(__METHOD__);
    }
    public function offsetExists($var) {
        var_dump(__METHOD__);
        if ($var == "foobar") {
            return true;
        }
        return false;
    }
    public function offsetUnset($var) {
        var_dump(__METHOD__);
    }
    public function offsetGet($var) {
        var_dump(__METHOD__);
        return "value";
    }
}
$obj = new obj;
echo "Runs obj::offsetExists()\n";
var_dump(isset($obj["foobar"]));
echo "\nRuns obj::offsetExists() and obj::offsetGet()\n";
var_dump(empty($obj["foobar"]));
echo "\nRuns obj::offsetExists(), *not* obj:offsetGet() as there is nothing to get\n";
var_dump(empty($obj["foobaz"]));
?>

以上例程的输出类似于：

Runs obj::offsetExists()
string(17) "obj::offsetExists"
bool(true)
Runs obj::offsetExists() and obj::offsetGet()
string(17) "obj::offsetExists"
string(14) "obj::offsetGet"
bool(false)
Runs obj::offsetExists(), *not* obj:offsetGet() as there is nothing to get
string(17) "obj::offsetExists"
bool(true)

Note that even though isset/empty works on classes implementing ArrayAccess, array_key_exists does not. At least not in PHP 5.3.

It seems that in PHP 7, if this method returns FALSE then offsetGet() will return NULL (in PHP 5, offsetGet() didn't first check what value offsetExists() returned). So if your code suddenly stops working when you upgrade to PHP 7 make sure that offsetExists() returns a sensible value!

If you care about key-strictness, you may need to use an alternative solution (maybe overriding offsetExists() in subclass(es)). So, offsetExists() acts like array_key_exists() and does not handle the key types. Here;
<?php
$array = ['one', 'two', 3.=>'boom!'];
$arrayObject = new ArrayObject($array);
$key = '3';
var_dump(array_key_exists($key, $array)); // bool(true)
var_dump(in_array($key, array_keys($array), true)); // bool(false)
var_dump($arrayObject->offsetExists($key)); // bool(true)
var_dump(in_array($key, array_keys($arrayObject->getArrayCopy()), true)); // bool(false)
// @override;
public function offsetExists($key)
{
  // make a strict check
  return in_array($key, array_keys($this->getArrayCopy()), true);
}
?>