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Date: Wed, 20 Feb 2008 20:53:34 +0000
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Subject: Re: [PHP-DEV] RFC: Traits for PHP
From: foolistbar@googlemail.com (Geoffrey Sneddon)


On 20 Feb 2008, at 20:28, Lars Strojny wrote:

> Am Mittwoch, den 20.02.2008, 20:14 +0000 schrieb Geoffrey Sneddon:
> [...]
>> Is there any reason why we cannot support multiple inheritance (which
>> some other languages already do)? The only thing that needs to be
>> clearly defined is sorting order. This avoids trying to create some
>> entirely new functionality to do something where we can simply extend
>> what we already do.
>
> Did you read the academic paper about the purpose of traits? In short:
> traits fix the common misconceptions of multiple inheritance. The most
> common problem is risky and fragile hierarchies. Also traits do the
> right thing[tm]: they allow compositions, not uncontrolable hotchpotch
> architectures.

Oh, wait. The previous email I was going to send in this thread was  
still a draft. That explains why that comment makes so little sense :)

What I was going to say is that how is something like:

<?php
trait foo {
	function output() {
		echo 'foo';
	}
}

trait bar {
	function output() {
		echo 'bar';
	}
}

class foobar {
	use foo;
	use bar;
}
?>

Better than:

<?php
class foo {
	function output() {
		echo 'foo';
	}
}

class bar {
	function output() {
		echo 'bar';
	}
}

class foobar extends foo, bar {
}
?>

Both are ambiguous if there is no documented conflict resolution: just  
because there's a proposal for traits doesn't mean you can't clearly  
define conflict resolution for multiple inheritance. I don't see  
either being intrinsically better than the other (and yes, I have read  
the papers about both).


--
Geoffrey Sneddon
<http://gsnedders.com/>