Strange behavior with array as static class property

Question

Can I have an associative array as a property of a class?

I have been trying but I get very strange results on something like this:

class MyClass {
  public static $quality = array('blue' => 20, 'green' => 30, 'yellow' => 40);
  public $car = array();
  public $bus = array();

  function __construct() {
     foreach(self::$quality as $key => $value) {
         $this->car[$key] = $value;
         $this->bus[$key] = $value;
         echo $this->car[$key] . '<br />';
         echo $this->bus[$key] . '<br />';
     }
     foreach(self::$quality as $key => $value) {
         echo $this->car[$key] . ' - ' . $this->bus[$key] . '<br />';
     }
  }
}

I am expecting this output:

but instead, I'm getting:

That's it. Only green and yellow bus miss the second digit...

And in a different point in my class, when I have something like this:

$attrib = 'bus';
$index = 'blue';
echo $this->$attrib[$index];

I get

Undefined Property MyClass::$b

Any hints on what I'm doing wrong? Or PHP doesn't accept associative arrays as properties of classes? Any help will be greatly appreciated.

Here is the code I isolated. If you run this PHP by itself you should get the strange behavior...

<?php
    ini_set('display_errors',1);
    error_reporting(E_ALL);

    class Session 
    {
        public static $per_page_count = array('photo' => 8 ,'book' => 20, 'road' => 30, 'lodge' => 30, 'tag' => 50);
        public $current_page = array();
        public $per_page = array();
        public $total_count = array();

        function __construct()
        {
            foreach (self::$per_page_count as $page_key => $page_count)
            {
                if (isset($this->per_page[$page_key])) 
                {
                    if ($this->per_page[$page_key] == '') $this->per_page[$page_key] = $page_count;
                }
                else  $this->per_page[$page_key] = $page_count;
                if (isset($this->current_page[$page_key]))
                {
                    if ($this->current_page[$page_key] == '') $this->current_page[$page_key] = 1;
                }
                else $this->current_page[$page_key] = 1;
                $this->total_count[$page_key] = 1;
            }
        }

        public function get_set($attribute,$index='',$value='')
        {
            echo '<br />before - '.$attribute.'-'.$index.'-'.$value.'<br />';
            if (trim($value) != '')
            {
                if (property_exists($this,$attribute))
                {
                    $this->$attribute['aaa'] = 50;
                    if ($index != '')
                    {
                        $_SESSION[$attribute][$index] = $value;
                        $this->$attribute[$index] = $value;
                    }
                    else
                        $_SESSION[$attribute] = $this->$attribute = $value;

                    $arraykey = array_keys($this->$attribute);
                }
            }
            else
            {
                if ($index != '')
                    return $this->$attribute[$index];
                else
                    return $this->$attribute;
            }
            echo '<pre>';
            print_r($this);
            echo '</pre>';
            echo '<br />after - '.$attribute.'-'.$index.'-'.$value.'<br />';
            echo '<br />variable - '.$this->$attribute[$index].'-'.$value.'<br />';
        }
    }

    $session = new Session();
    $session->get_set('current_page','photo',4);
    $session->get_set('total_count','photo',150);
?>

At the bottom, you see that I call get_set() twice and each time, instead of setting the property inside the class, it creates a new property.

What am I doing wrong? A appreciate any help.

Your code seems to work fine for me, other than a few syntax errors: http://codepad.viper-7.com/2rt3hT — The Maniac, Dec 09 '11 at 23:55
Associative arrays as properties is fine. Can you post the actual code? Difficult to debug code you've just typed in and has been edited. — webbiedave, Dec 09 '11 at 23:55

score 0 · Answer 1 · answered Dec 10 '11 at 01:20

Wrong:

$attrib = 'bus';
$index = 'blue';
echo $this->$attrib[$index];

Correct:

$attrib = 'bus';
$index = 'blue';
$hash = $this->$attrib
echo $hash[$index];

What's happening in the wrong version? First, it's possible to lookup a character in a string by position. For instance:

$str = 'abcdefg';
echo $str[1];  // outputs 'b'

$attrib[$index] is being evaluated first. PHP is treating $index as a numeric index for the $attrib string, with $index being cast to a number (in PHP 'blue' == 0). Since $attrib[0] == 'b', PHP is looking for $this->b hence the Undefined property error.

Thank you very much. Your solution worked. I had a guess that this was the problem but I think my brain was too tired to see the solution. Thank you very much again. — Dentra Andres, Dec 10 '11 at 04:31

Strange behavior with array as static class property

1 Answers1