Hi Greg,
There is no reason why you can't still use the current method to implement
your variations to the singleton design pattern. But, yes, I am proposing
that the strict "text book" variety is implemented.
If you haven't had the need to singleton-ize more than 2-3 classes, you
probably haven't worked with tiered architecture, or haven't thought to use
singleton in this situation.
The way I work is with two-tiered architecture. I have a presentation tier
which consists of HTML and php which renders the HTML. I then have a second
tier which is a data access tier. In the data access tier, I have one class
for each database table. In these classes there are SQL statements for
saving, retrieving records, in fact any operation that I do to the table.
No SQL resides outside of the table's data access class. Each one of these
classes is a singleton.
There are two things that a native singleton implementation would solve:
- At the data access layer, it is nasty to duplicate the singleton pattern
for each class, (or worse, work with strings for class names).
- From the presentation layer, it is ugly to work with the data access
singletons.
Example: A page in the presentation tier which lists all news posts
<?php foreach(getInstance('content_news_items')->getAll() as $post){ ?>
<h1><?php echo($post['news_item_heading']) ?></h1>
<p><?php echo($post[' news_item_contents']) ?></p>
<?php } ?>
It would be nicer (and much more efficient) to be able to go:
<?php foreach(content_news_items->getAll() as $post){ ?>
<h1><?php echo($post['news_item_heading']) ?></h1>
<p><?php echo($post[' news_item_contents']) ?></p>
<?php } ?>
I actually have about 50 singleton classes in my current project, and trust
me, they are all warranted. I have put a copy of a screen shot of my
eclipse project at: http://hlrally.net/media/content_pages/gotsingleton.png
I put a blue line next to the singleton classes. The folder "components"
represents the data access layer. The presentation layer is not seen in
that shot.
Now we all have different programming styles and use different architectural
principles to each other. Just remember this is not a debate about what
architecture is better etc. I am just showing an example.
Scott
-----Original Message-----
From: Gregory Beaver [mailto:[EMAIL PROTECTED]
Sent: Tuesday, 6 March 2007 4:12 PM
To: [EMAIL PROTECTED]
Cc: [EMAIL PROTECTED]; 'Guilherme Blanco'; internals@lists.php.net
Subject: Re: [PHP-DEV] Native Singleton Implementation
Peter Hodge wrote:
> You should just need to:
> - add T_SINGLETON to the parser.
> - add an is_singleton flag for class definitions, activated by
T_SINGLETON.
> - overload the 'new' operator to retrieve from the hash table if the class
is a
> singleton (otherwise call __construct() as normal).
> - implement some of those helper functions such as singleton_getobjects().
Hi,
This seems both to be excessively magical and inflexible. For instance,
I have implemented global singletons, singleton per-configuration path
(i.e. for a configuration object with cascading configuration files, one
singleton per configuration file location), and other models for
singleton that stray on the continuum between singleton and factory.
The proposed implementation allows only the textbook singleton.
The benefit of having singleton in the zend engine in my book is zero.
If you have 10 gazillion classes that are all singletons, perhaps
another look at the design is in order? I've never had to singleton-ize
more than 2-3 classes in even the most complex projects I've been
involved with.
Greg
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