ArrayAccess::offsetExists

(PHP 5, PHP 7, PHP 8)

ArrayAccess::offsetExists — Indique si une position existe dans un tableau

Description

public ArrayAccess::offsetExists(mixed $offset): bool

Indique si une position existe.

Cette méthode est exécutée lorsque la fonction isset() ou empty() est appliquée à un objet qui implémente l'interface ArrayAccess.

Note:
Lors de l'utilisation de empty(), ArrayAccess::offsetGet() est appelé et vérifie si la valeur est vide, uniquement si ArrayAccess::offsetExists() retourne true.

Liste de paramètres

offset: Une position à vérifier.

Valeurs de retour

Cette fonction retourne true en cas de succès ou false si une erreur survient.

Note:
La valeur retournée sera transtypée en booléen si une valeur non booléenne est retournée.

Exemples

Exemple #1 Exemple avec 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 "Exécute obj::offsetExists()\n";
var_dump(isset($obj["foobar"]));

echo "\nExécute obj::offsetExists() et obj::offsetGet()\n";
var_dump(empty($obj["foobar"]));

echo "\nExécute obj::offsetExists(), *et non pas* obj:offsetGet() car il n'y a rien à lire\n";
var_dump(empty($obj["foobaz"]));
?>

Résultat de l'exemple ci-dessus est similaire à :

Exécute obj::offsetExists()
string(17) "obj::offsetExists"
bool(true)

Exécute obj::offsetExists() et obj::offsetGet()
string(17) "obj::offsetExists"
string(14) "obj::offsetGet"
bool(false)

Exécute obj::offsetExists(), *et non pas* obj:offsetGet() car il n'y a rien à lire
string(17) "obj::offsetExists"
bool(true)

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User Contributed Notes 2 notes

down

nicosp at gmail dot com ¶

3 months ago

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=41727

down

pierstoval at gmail dot com ¶

11 months ago

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;

?>

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