The Case of the Null Reference: Code Listing 3

Referecnes.php

<?php

class NaturalNumber {
  private $n;
  
  public function __construct(int &$n) {
    if ($n < 1) {
      throw new InvalidArgumentException('n must be greater than zero, got ' . $n);
    }
    
    $this->n =& $n;
  }
  
  public function toInt(): int {
    return $this->n;
  }
}

$n   = 42;
$nat = new NaturalNumber($n);
$n   = null;

$nat->toInt();