privateなプロパティにアクセスできるのか！！！

test.php

<?php

class Category 
{
  private $id;
  
  public function __construct($id)
  {
    $this->id = $id;
  }
  
  public function equals(Category $category): bool
  {
    return $this->id === $category->id;
  }
}

$c1 = new Category(1);
$c2 = new Category(1);

var_dump($c1->equals($c2));