<?php
class rectangle {
  protected $w;
  protected $h;
  
  // Constructor
  public function __construct($width = 0, $height = 0) {
    $this->w = $width;
    $this->h = $height;
  }
  // Convert to string
  public function __toString() {
  return "width:  " . $this->w . "\n" . 
         "height: " . $this->h . "\n" . "\n";
  }
  // Calculate rectangle area
  public function area() {
    return $this->w * $this->h;
  }
  // Other method (not rilevant)
  // ...
  
  public static function order(&$rectangles) {
    uasort($rectangles, 'rectangle::order_info');
  }
  private static function order_info(rectangle $a, rectangle $b) {
    if ($a->area() < $b->area())
    {
      return -1;
    }
    else
    {
      return 1;
    }
  }
}

$rectangles = array();
for($i = 0; $i < 10; $i++ )
{
  $width  = rand(1, 100);
  $height = rand(1, 100);
  
  $rec = new rectangle($width, $height);
  
  $rectangles[$rec->area()] = $rec;
}

print_r($rectangles);
rectangle::order($rectangles);
print_r($rectangles);