====== Request for Comments: SPL weak type hinting ======
  * Version: 1.0
  * Date: 2010-05-31
  * Author: Ferenc Kovacs <tyra3l at gmail dot com>
  * Status: Draft
  * First Published at: http://wiki.php.net/rfc/splweaktypehintingwithautoboxing
  * Other formats ..


===== Introduction =====
This rfc tries to propose an alternative solution for type hinting in PHP.
Basically its a weak type hinting(auto type conversion if possible without data loss), with support for scalars*, implemented as an spl interface.

* You hint the matching Spl classname instead of the scalar name, the weak type hinting will kick-in and validate/convert the passed argument into the Spl type, but it can be used as a scalar thanks to the behaviour provided by the SplType.

===== Why weak type hinting? =====
See http://wiki.php.net/rfc/typecheckingstrictandweak

===== Why support type hinting for scalars? =====
See http://wiki.php.net/rfc/typecheckingweak

===== Why should we throw Exteption instead of trigger_error? =====
From the perspective of the API developer, E_STRICT or similar low priority notices cannot guarantee, that the API consumer is noticed about the invalid argument.
From the perspective of the API consumer, for catching the E_STRICT is either require adding/modifying a global error handler, or using the @ to suppress the error and call error_get_last to check for error, which is just hackish. 

===== Proposal =====
Currently, there is no support for hinting scalar types, and only strict type hinting is allowed (there is no conversion).

The idea is that we could introduce a new Spl interface, which supports the following behaviour:
- if the hinted argument type and the passed argument type is different, but the type conversion can be done without data loss, then convert the argument into the hinted type.
- if the hinted argument type and the passed argument type is different, and cannot be converted without data loss, then throws a InvalidArgumentException.


===== Examples =====
<code php>
class foo implements WeakTypeHinting{
  public function bar(SplInt $baz){
    return ++$baz;
  }
}

$foo = new foo;
echo $foo->bar(1);
// 2
echo $foo->bar('2');
// 3
echo $foo->bar('3a')
// InvalidArgumentException 
</code>

===== Notes =====
If an object implements ArrayAccess spl interface, it could be handled as an array(eg. if you hinted array, you can pass ArrayObject).