dest =& $dest; } /** @var mixed */ protected $dest; function exists(): bool { return $this->dest !== null; } function available(): bool { return $this->exists(); } function get($default=null) { if ($this->dest === null) return $default; else return $this->dest; } function set($value): void { $this->dest = $value; } function del(): void { $this->dest = null; } }