[E014] Error: missing type for readonly property `foo::$e`
   ,-[code.php:5:26]
   |
 3 | class foo {
   *       ^^^  
   *             
   * 
 5 |         public readonly &$e,
   *                ^^^^^^^^  ^|  
   *                           `-- try adding a type before `$e`
   *                              
   *                               
---'