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To: internals@lists.php.net,troels knak-nielsen <troelskn@gmail.com>
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Date: Thu, 09 Jul 2009 19:28:35 -0500
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Subject: Re: [PHP-DEV] Type hinting - Request for Discussion
From: spam.goes.in.here@gmail.com (Josh Thompson)

troels knak-nielsen wrote:
> 1) It covers all the use cases for a type-based system (You can use
> `is_integer` as a contract, if you want that)
> 2) It's extensible in user-space, which means that it can be used to
> convey much more accurate information, relevant to the application
> needs.
> 3) It's focused on the interface of input-parameters, rather than their type.

This is my favorite alternative so far. There are just a few problems 
with parsing as I see it.

  - How do you know if it is a contract or the current object type hint?
  - It doesn't allow a type to be forced (casted) to the correct type.

To address these items, I suggest the following changes.

Change the syntax of the contract to look like a function call (which is 
essentially what we are doing):

   <?php
   function array_of_numeric($x)
   {
       if (!is_array($x)) {
           return false;
       }
       foreach ($x as $val) {
           if (!is_numeric($val)) {
               return false;
           }
       }
       return true;
   }

   function sum(array_of_numeric($a)) {
       return array_sum($a);
   }

This could even be extended to allow for more generic types by allowing 
constant parameters for the contract:

   <?php
   function array_of($x, $type)
   {
       if (!is_array($x)) {
           return false;
       }
       switch ($type) {
           case 'int':
               $check = 'is_int';
               break;
           case 'float':
               $check = 'is_float';
               break;
           case 'numeric':
               $check = 'is_numeric';
               break;
           case 'string':
               $check = 'is_string';
               break;
           case 'bool':
               $check = 'is_bool';
               break;
           default:
               return false;
       }
       foreach ($x as $val) {
           if (!$check($val)) {
               return false;
           }
       }
       return true;
   }

   function sum(array_of($a, 'numeric')) {
       return array_sum($a);
   }

To allow for casting, the contract function could take the value by 
reference and cast it:

   <?php
   function array_of_float(&$x)
   {
       if (!is_array($x)) {
           return false;
       }
       foreach ($x as $key => $val) {
           if (!is_numeric($val)) {
               return false;
           }
           $x[$key] = (float)$val;
       }
       return true;
   }

   function sum(array_of_float($a)) {
       return array_sum($a);
   }

-- 
Joshua Thompson
Mechanical Engineer/Software Developer
http://www.schmalls.com