# Request for Comments: Horizontal Reuse for PHP

- Thread: https://externals.io/message/41860
- Original archive: https://news-web.php.net/php.internals/41860
- Started by Alan Pinstein on 2008-11-12T01:41:07+00:00
- Messages: 2
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## #41860 — Alan Pinstein — 2008-11-12T01:41:07+00:00

URL: https://externals.io/message/41860#41860

I was pointed to the http://wiki.php.net/rfc site the other day at the  
ATLPHP user group and found the traits and related RFC's.

I just read the RFC on grafts and traits for PHP. Great ideas! There  
is one other thing I'd like you to take a look at as well though,  
that's very useful.

Objective-C has a construct called a Category. It is similar in  
functionality to Traits, but has an important and useful distinction
in the way that the additional functions are "injected" into the  
target class in practice.

Categories can be applied to existing classes from *outside* the class  
definition. This is a very useful pattern in that it allows users of  
classes to inject functionality without subclassing, AND without  
touching the source of the target class.

class Helloworld
{
    public function sayHello() { print "HELLO"; }
}

category HelloworldExtras on Helloworld
{
    public function sayWorld() { print "World"; }
}

$h = new Helloworld;
$h->sayWorld(); // print "WORLD"

This is extremely beneficial for lightweight "extension" of classes  
without subclassing.

Other than this, it is identical to traits.

I was discussing this off-list with Stefan, and he asked me how it  
would work with autoloading, which has led me to add one more piece to  
the idea, which is a way to tell the compiler to load your category. I  
haven't thoroughly read all of the namespace RFCs so this may conflict  
with the "use" keyword, but something like:

use HelloworldExtras;

Would be a lightweight way to make sure that the autoloader would add  
the category into the runtime.

Looking forward to your comments. Also, I will be at php|works in  
Atlanta Thursday and Friday if anyone is interested in discussing this  
in person!

Regards,
Alan Pinstein


Regards,
Alan Pinstein
http://phocoa.com

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## #41862 — Stan Vassilev | FM — 2008-11-12T03:17:27+00:00

URL: https://externals.io/message/41860#41862 · In reply to: #41860

> class Helloworld
> {
>    public function sayHello() { print "HELLO"; }
> }
>
> category HelloworldExtras on Helloworld
> {
>    public function sayWorld() { print "World"; }
> }
>
> $h = new Helloworld;
> $h->sayWorld(); // print "WORLD"
>
> This is extremely beneficial for lightweight "extension" of classes 
> without subclassing.

This feature is identical to the C# .NET "Extension" methods. The best use 
of it is for selectively extending the primitive type classes on the fly 
with methods you need (string, int, array, etc.).

The irony in this is, in PHP the primitive types are not OOP capable, so 
with this in mind I wonder how much this functionality would serve to make 
the life of people easier, and how much of it will be just the rope they 
need to hang themselves. The concept of categories and extensions is not as 
popular to the average developer as say classes and interfaces.

Also we can't overload "use" for this as "use" specifically only imports 
symbol names, not actual code, into the environment. It doesn't have the 
knowledge of whether something is a namespace, or a class, or a category, so 
to know how to trigger autoload.

Regards, Stan Vassilev