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Date: Tue, 29 Apr 2008 17:51:30 +0200
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Thread-Topic: Re: [PHP-DEV] Class Properties in Interfaces?
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To: <internals@lists.php.net>
Subject: RE: Re: [PHP-DEV] Class Properties in Interfaces?
From: johncart@cisco.com ("John Carter -X (johncart - PolicyApp Ltd at Cisco)")

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The article explicitly mentions OOP interfaces in a few languages. But
the article, or for that matter any formal definition of an interface
isn't really what I asked about:
=20
My question was simply: why can't interfaces have properties?
=20
John.

________________________________

From: Nathan Nobbe [mailto:quickshiftin@gmail.com]=20
Sent: 29 April 2008 16:17
To: John Carter -X (johncart - PolicyApp Ltd at Cisco)
Cc: internals@lists.php.net
Subject: Re: Re: [PHP-DEV] Class Properties in Interfaces?


On Tue, Apr 29, 2008 at 6:28 AM, John Carter -X (johncart - PolicyApp
Ltd at Cisco) <johncart@cisco.com> wrote:


=09
	I think I must be missing something here, but this sounds a
little
	tautological - "we can't do it because it doesn't make sense.
This is
	because it doesn't make sense"
=09
	Certainly most people (myself included) consider interfaces to
be
	methods only, but I can't find a reason why not, and a
	search-on-wikipedia-instead-of-doing-proper-research appears to
allow
	it:
http://en.wikipedia.org/wiki/Interface_%28computer_science%29


the problem with that article, as it pertains to this conversation is
that it is referring to interfaces as a general concept.  'interfaces'
can be formed in many ways, via extension of an abstract class or even
an expected set of a parameters in an HTTP request...
getting to the more concrete term 'interface' as it pertains to a
language keyword, interfaces define a contract; they do not specify
implementation details.  member variables only facilitate the actions
member functions expose and therefore, they are part of the
implementation.

additionally, one can look to java (and likely others) to see that
public attributes are not supported on interfaces. here is a definition
from a java5 cert book;
"When you create an interface, you're defining a contract for *what* a
class can do, without saying anything about how the class will do it.
An interface is a contract."

-nathan


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