ArrayAccess::offsetExists

(PHP 5, PHP 7, PHP 8)

ArrayAccess::offsetExists — Comprobar si existe un índice

Descripción

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

Comprueba si existe o no un índice.

Este método se ejecuta cuando se utilizan las funciones isset() o empty() sobre los objetos que implementan ArrayAccess.

Nota:
Cuando se utiliza empty(), ArrayAccess::offsetGet() será invocada para comprobar si está vacío solamente si ArrayAccess::offsetExists() devuelve true.

Parámetros

offset: El índice a comprobar.

Valores devueltos

Devuelve true en caso de éxito o false en caso de error.

Nota:
El valor de retorno se debe convertir a bool si no devuelve un valor boleano.

Ejemplos

Ejemplo #1 Ejemplo de 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 "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"]));
?>

El resultado del ejemplo sería algo similar a:

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)

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User Contributed Notes 1 note

down

pierstoval at gmail dot com ¶

3 days 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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