Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:44616
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Message-ID: <8C.99.43450.5A5EB4A4@pb1.pair.com>
To: internals@lists.php.net
Date: Wed, 01 Jul 2009 17:39:35 -0500
User-Agent: Thunderbird 2.0.0.18 (Windows/20081105)
MIME-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Subject: RFC: Boxing and Unboxing
From: spam.goes.in.here@gmail.com (Josh Thompson)

Greetings All,

Intro
=====

The discussion over type hinting seems to be getting divided between 
those who really like it (most likely the ones who write strongly typed 
programs anyway) and those who don't want to add yet another kind of 
type system to PHP.

I have been thinking about it and wondered why we don't borrow a concept 
  from C# with a PHP twist of course. The basic idea of boxing in C# is 
that a value type is implicitly converted to an object type. Unboxing is 
  done explicitly to convert the object back to a value type.

Idea
====

I figure instead of adding scalar type hints, we could reuse the object 
type hints to do implicit boxing of variables. Either (but not both) a 
new magic method (``__box`` for example) or a new interface (``Boxable`` 
for example) would need to be added to PHP. The method would accept the 
scalar value and set its internal representation (similar to 
``__wakeup``). The method could either (but not both) return false or 
throw an exception (``BoxingException`` for example).

It is my belief that PHP would need to include as many object versions 
of scalar types as possible. The boxing functionality could be added to 
the SPL Types [1]_ to provide for standard representations of the scalar 
types. However the power to box variables would also be available in 
userland classes.

The unboxing of variables would need to occur on an explicit cast or on 
a call to an internal function. The unboxing could be implemented as the 
RFC for class casting to scalar [2]_. It already discusses some examples 
for a new magic method or interface. I propose some more to relate to 
the unboxing concept (``__unbox`` for a magic method, and ``Unboxable`` 
for an interface).

Benefits
========

The benefits to boxing and unboxing include:

  - Only minor modifications required to the current type-hinting
    implementation (I am only assuming this part).
  - The boxing and unboxing ability can be used in userland classes
    to accomplish "cool things".
  - Get SplTypes and scalar casting in PHP core.
  - Probably more that I can't think of off the top of my head.

Patch
=====

I have very limited C skills, so no patch exists.

.. [1] `SPL Types <http://.php.net/manual/en/book.spl-types.php>`_
.. [2] `RFC: Class casting to scalar 	
	<http://wiki.php.net/rfc/class_casting_to_scalar`_

Thanks,

-- 
Joshua Thompson
Mechanical Engineer/Software Developer
http://www.schmalls.com