sealed-class.php

<?php

sealed class Token {
    public bool $isSignificant;
  
    class Identifier {
       public function __construct(public string $name) {
           $this->isSignificant = true;
       }
    }
    class Whitespace() {
       public function __construct() {
           $this->isSignificant = true;
       }
    }
    class Comment() {
       public function __construct(public string $comment) {
           $this->isSignificant = false;
       }
    }
}