Least sloppy way to enforce allowable values or ranges for class properties

Question

Say hypothetically I have a class...

class Main {

    $prop1 = 2;
    $prop2 = 23;
    ...
    $prop42 = "what";

    function __construct($arg_array) {
        foreach ($arg_array as $key => $val) {
            $this->$key = $val;
            }
        }
    }

Say I create and object...

$attributes = array("prop1"=>1, "prop2"=>35235, "prop3"=>"test");
$o = new Main($attributes);

Providing for default property values if not supplied by the user is obvious. But what if I want to enforce arbitrary limits on user supplied values for object properties? What if I want to enforce $prop1 to be of int, be no less than 1, and be no greater than 5. And, $prop42 to be of type string, no less than 'A', and no greater than 'Z'? For this purpose, what would be the cleanest way, keeping the script as short and sweet as possible, using any possible language feature or trick?

I'm stuck in __construct() checking supplied values against a rule array built like so...

$allowable = array(
    "prop1" => array(
        'type' => 'int',
        'allowable_values' => array(
            'min' => 1,
            'max' => 5
            )
        ),
    "prop2" => array(
        'type' => 'int',
        'allowable_values' => array(
            1,
            235,
            37,
            392,
            13,
            409,
            3216
            )
        ),
    ...
    "prop42" => array(
        'type' => 'string',
        'allowable_values' => array(
            'min' => 'A',
            'max' => 'Z'
            )
        )
    );

As you can see by prop2, my validation function is starting to get pretty messy with so many 'if-then-iterate-again' blocks as I have to account for not only ranges but a list of permitted values. With the validation code and this rule array, my script is getting rather bulky.

The question is, how can I structure my class or class properties or the validation code or any other aspect of my script to be as short and concise as possible to allow property range and value enforcement? Is there a language feature or trick to handle this more elegantly? Have I reached a brick wall, the limit of this language? Are there any examples from other languages that can easily implement this which can provide some clue?

Answer 1

I ran into a similar issue the other day. Here's what I would do:

   private $props;
   private $rules; 

   function __construct($params) {

      // or you can get the rules from another file, 
      // or a singleton as I suggested

      $this->rules = array (array('type' => 'range', 'min' => 10, 'max' => 20), 
        array('type' => 'in_set', 'allowed' => array(1,2,3)));

      for ($i=0; $i<count($params); $i++) {

         if ($this->check($params[$i], $this->rules($i))
            $this->props[$i] = $params[$i];
         else
            throw new Exception('Error adding prop ' . $i);
      }

   }


   function check($value, $rule) {
      switch($rule['type']) {
         case 'range':
            return ($rule['min'] <= $value && $value <= $rule['max']);  

         case 'in_set':
            return (in_array($value, $rule['allowed']));

         // and so on
      }
   }

If you have many parameters, you can use an array and iterate through that. If your validation rules are always going to be the same, you can put them in a separate file and load that in your constructor or whatever.

EDIT: By the way, there is really no point in testing type in PHP. It is both not very reliable and unnecessary.

EDIT 2: Instead of having a global variable with the rules, you can use a Singleton:

Answer 2

getters and setters

class Main {
  private $prop1;
  private $prop2;
  private $prop3;

  public function __construct( $p1 , $p2 , $p3 )
  {
    $this->setProp1($p1);
    $this->setProp2($p2);
    $this->setProp3($p3);
  }

  public function setProp1($p1)
  {
    // conditional checking for prop1
    if(!$ok) throw new Exception('problem with prop1');
    $this->prop1 = $p1;
  }

  //.. and so on
}