00-sealed-class.php

<?php

sealed class Token {
    abstract public function isSignificant(): bool;
  
    class Identifier {
       public function __construct(public string $name) {}
       public function isSignificant(): bool { return true; }
    }
    class Whitespace() {
       public function isSignificant(): bool { return false; }
    }
    class Comment() {
       public function __construct(public string $comment) {}
       public function isSignificant(): bool { return false; }
    }
}

01-union-type.php

<?php

union Token {
    case Identifier(public string $name);
    case Whitespace;
    case Comment(public string $comment);

    public function isSignificant(): bool {
        return match($this) {
            self::Identifier => true,
            self::Whitespace => false,
            self::Comment => false
        };
    }
}

02-enhanced-enum.php

<?php

enum Token {
    case Identifier(public string $name) = self(true);
    case Whitespace = self(false);
    case Comment(public string $comment) = self(false);

    protected function __construct(private bool $isSignificant) {}
  
    public function isSignificant(): bool {
        return $this->isSignificant;
    }
}

03-enum-with-implicit-parent-constructor.php

<?php

enum Token {
    protected function __construct(private bool $isSignificant) {}
  
    case Identifier(true) {
       public function __construct(public string $name) {}
    };
    case Whitespace(false);
    case Comment(false) {
       public function __construct(public string $comment) {}
    };
  
    public function isSignificant(): bool {
        return $this->isSignificant;
    }
}