backedEnumArrayAccess.php

<?php

/**
 * @implements ArrayAccess<BackedEnum|array-key, mixed>
 */
class Foobar implements ArrayAccess
{
    /**
     * @param array<array-key, mixed> $members
     */
    public function __construct(private array $members) {}

    private function filterKey(BackedEnum|string|int $key): string|int
    {
        return match (true) {
            $key instanceof BackedEnum => $key->value,
            default => $key,
        };
    }

    /**
     * @param BackedEnum|array-key $offset
     */
    public function offsetExists(mixed $offset): bool
    {
        return array_key_exists($this->filterKey($offset), $this->members);
    }

    /**
     * @param BackedEnum|array-key $offset
     */
    public function offsetGet(mixed $offset): mixed
    {
        return $this->members[$this->filterKey($offset)] ?? throw new OutOfBoundsException('Member not found');
    }

    /**
     * @param BackedEnum|array-key $offset
     */
    public function offsetUnset(mixed $offset): void
    {
        unset($this->members[$this->filterKey($offset)]);
    }

    /**
     * @param BackedEnum|array-key|null $offset
     */
    public function offsetSet(mixed $offset, mixed $value): void
    {
        if (null !== $offset) {
            $this->members[$this->filterKey($offset)] = $value;

            return;
        }

        $this->members[] = $value;
    }
}

enum Attr: string
{
    case Foo = 'foo';
    case Bar = 'bar';
    case Toto = 'toto';
}

$obj = new Foobar(['foo' => 1, 'bar' => 2, 'baz' => 3]);
$obj[Attr::Toto] = 'tata';
var_dump(
    $obj[Attr::Foo],
    isset($obj[Attr::Bar])
);