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<?php declare(strict_types=1); class Foo { private array $data = []; public function __set(string $name, $value): void { $this->data[$name] = $value; } public function __isset(string $name): bool { return isset($this->data[$name]); } public function __unset(string $name): void { unset($this->data[$name]); } } $foo = new Foo(); $one = 1; $two = 2; $foo->$one = 'one'; $foo->$two = 'two'; var_dump( isset($foo->$one), // true isset($foo->$two) // true ); unset($foo->$one); var_dump( isset($foo->$one) // false );