(PHP 5, PHP 7, PHP 8)
ArrayAccess::offsetExists — Verifica se uma posição existe
Verifica se uma posição existe ou não.
Este método é executado ao utilizar-se a função isset() ou empty() em objetos que implementem ArrayAccess.
Nota:
Ao utilizar a função empty(), o método ArrayAccess::offsetGet() será chamado e checado por vazio somente se o método ArrayAccess::offsetExists() retornar
true
offsetUma posição a ser checada.
Retorna true em caso de sucesso ou false em caso de falha.
Nota:
O valor de retorno será convertido para bool se um não booleano for retornado.
Exemplo #1 Exemplo do método ArrayAccess::offsetExists()
<?php
class obj implements ArrayAccess {
public function offsetSet($offset, $value): void {
var_dump(__METHOD__);
}
public function offsetExists($var): bool {
var_dump(__METHOD__);
if ($var == "foobar") {
return true;
}
return false;
}
public function offsetUnset($var): void {
var_dump(__METHOD__);
}
#[\ReturnTypeWillChange]
public function offsetGet($var) {
var_dump(__METHOD__);
return "value";
}
}
$obj = new obj;
echo "Executa obj::offsetExists()\n";
var_dump(isset($obj["foobar"]));
echo "\nExecuta obj::offsetExists() e obj::offsetGet()\n";
var_dump(empty($obj["foobar"]));
echo "\nExecuta obj::offsetExists(), *não executa* obj:offsetGet()\n";
var_dump(empty($obj["foobaz"]));
?>O exemplo acima produzirá algo semelhante a:
Executa obj::offsetExists() string(17) "obj::offsetExists" bool(true) Executa obj::offsetExists() e obj::offsetGet() string(17) "obj::offsetExists" string(14) "obj::offsetGet" bool(false) Executa obj::offsetExists(), *não executa* obj:offsetGet() string(17) "obj::offsetExists" bool(true)
PHP implementation of isset() will only call offsetExists and will never check offsetGet for null.
This is not 100% clear from the docs.
Relevant bug:
https://bugs.php.net/bug.php?id=41727Please 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;
?>