ArrayAccess::offsetExists
(PHP 5 >= 5.0.0)
ArrayAccess::offsetExists — Whether a offset exists
Description
Whether or not an offset exists.
This method is executed when using isset() or empty() on objects implementing ArrayAccess.
Note:
When using empty() ArrayAccess::offsetGet() will be called and checked if empty only if ArrayAccess::offsetExists() returns
TRUE.
Parameters
-
offset -
An offset to check for.
Return Values
Returns TRUE on success or FALSE on failure.
Note:
The return value will be casted to boolean if non-boolean was returned.
Examples
Example #1 ArrayAccess::offsetExists() example
<?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"]));
?>
The above example will output something similar to:
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)
Коментарии
Please note something:
The docs explain clearly that this method is called when "isset()" or "empty()" are called on the object's key.
This means that there is a huge difference in your custom implementation when you have an internal array on which you choose to call either "isset()" or "array_key_exists()".
Even though the method says "offsetExists", it is *not* supposed to be used only when the offset exists, because this is not at all the behavior of neither "isset" nor "empty" internally.
This means you can have issues like this (more explanations below):
<?php
class Value {
public function __construct(
public string $value,
) {
}
}
class MyArray implements ArrayAccess {
private array $internal = [];
public function offsetExists(mixed $offset): bool
{
return array_key_exists($offset, $this->internal);
}
// ... rest of the implementation
public function offsetGet(mixed $offset): mixed
{
return $this->offsetExists($offset) ? $this->internal[$offset] : null;
}
public function offsetSet(mixed $offset, mixed $value): void
{
if (is_null($offset)) {
$this->internal[] = $value;
} else {
$this->internal[$offset] = $value;
}
}
public function offsetUnset(mixed $offset): void
{
unset($this->internal[$offset]);
}
}
$object = new MyArray();
$object['key'] = null;
// This is where the error occurs:
// PHP Fatal error: Uncaught TypeError: Value::__construct(): Argument #1 ($value) must be of type string, null given
$otherValue = isset($object['key']) ? new Value($object['key']) : null;
?>
The thing here is that we have some code that cannot use the "??" operator because we need the output of the "isset" call to return true, and only then we want to use.
With a real array, this should be fairly common because we know how "isset" works.
However, since the "offsetExists" method has a lot of different implementations in PHP libaries, you should *not* trust the output in "isset" with objects implementing ArrayAccess.
A workaround is to create an intermediate variable and run "isset()" on it:
<?php
// Before
$otherValue = isset($arrayObject['key']) ? new Value($arrayObject['key']) : null;
// After
$rawValue = $arrayObject['key'] ?? null;
$otherValue = isset($rawValue) ? new Value($rawValue) : null;
?>