Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:28231
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: pass (pb1.pair.com: domain synergy8.com designates 202.174.102.10 as permitted sender)
Reply-To: <scott.mcnaught@synergy8.com>
To: "'Guilherme Blanco'" <guilhermeblanco@gmail.com>
Cc: <internals@lists.php.net>
References: <45E33990.8030806@adaniels.nl> <408821909.20070303232323@marcus-boerger.de> <fe05d1540703040446u201ce0b7we685bd50808e2c0c@mail.gmail.com> <1508893792.20070304144812@marcus-boerger.de> <fe05d1540703040629j21dc1442k4b2aee57f35d3ed3@mail.gmail.com> <592868326.20070304163838@marcus-boerger.de> <fe05d1540703040922j3d146a5bw7b10009283e02a87@mail.gmail.com> <26646995.20070304183706@marcus-boerger.de> <001e01c75e86$8043bce0$0900a8c0@scottnote> <001f01c75e86$fe96e900$0900a8c0@scottnote> <bcb7aa500703041220y376165b0s81d4294eb4bf047a@mail.gmail.com>
Date: Mon, 5 Mar 2007 15:12:44 +1000
Message-ID: <000301c75ee4$e9876ef0$0900a8c0@scottnote>
MIME-Version: 1.0
Content-Type: text/plain;
	charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
In-Reply-To: <bcb7aa500703041220y376165b0s81d4294eb4bf047a@mail.gmail.com>
Thread-Index: AcdeonyCuXmwfQ0DT7mfK4f3ebflOgAQOccg
Subject: RE: [PHP-DEV] Native Singleton Implementation
From: scott.mcnaught@synergy8.com

Sure, implementing singleton is easy enough.  But you can't abstract it =
in
PHP.

In C++ you can use things called template classes or generics to =
abstract
the singleton implementation. This way you don=92t have to duplicate the
protected constructor, the instance and the accessor for each class.

I guess I'm really talking about the bigger picture here, where you =
might
have an application which has around 50 singleton classes.  I don=92t =
want to
duplicate code in each one.

I have already implemented singleton in two different ways (see examples =
1
and 2 in the bug report - http://bugs.php.net/bug.php?id=3D39946) and =
they
both have drawbacks.

Hmm... give the bug report a quick read over again :)


-----Original Message-----
From: Guilherme Blanco [mailto:guilhermeblanco@gmail.com]=20
Sent: Monday, 5 March 2007 6:21 AM
To: scott.mcnaught@synergy8.com
Cc: internals@lists.php.net
Subject: Re: [PHP-DEV] Native Singleton Implementation

Hi,

The idea behing a native singleton class implementation should be
really handy, but this is fairly simple to achieve.

Take a look at PHP documentation to see some patterns implementation:
http://www.php.net/manual/en/language.oop5.patterns.php


I hope this helps.


Best regards,

On 3/4/07, scott.mcnaught@synergy8.com <scott.mcnaught@synergy8.com> =
wrote:
> *** Sorry - forgot to change the subject ***
>
> Hello All,
>
> I am new to the php internals mailing list.  I am a fairly experienced
> programmer with a few ideas floating around.  I have come from a C++ =
games
> development background and have now moved to primarily writing in php.
>
> One thing that I used extensively in C++ was the singleton design =
pattern.
> I assume that most of you know what that is, if not a quick google =
search
> will let you know.  I have written an implementation of singleton in =
php,
> but it's slow, and you have to use strings to reference the classes, =
or
> duplicate a lot of code. (See methods 1 and 2 below)
>
> I recently submitted an RFC to bugs.php.net about this, but there was
never
> feedback from the internals group, so I am going to try here.
>
> http://bugs.php.net/bug.php?id=3D39946
>
> In a few months time, I would like to start helping the development of
php,
> but I am too busy at the moment.
>
> I was wondering if anyone has the time to implement this winner =
feature.
I
> think it would encourage good programming practise and speed up a lot =
of
php
> apps.  Also I would like people's thoughts and feedback on the idea.
>
> If no-one can implement this before me, I will have a go at it in a =
few
> months time.
>
> Thankyou,
>
> Scott McNaught
>
>
>
> Description:
> ------------
> ###
> # Introduction
> ###
> This document is an RFC for adding a small patch to the zend engine to
> allow for native singleton classes.  The problem
> is that currently theres no clean way to implement singleton classes =
in
> user-land over the entirety of a project.
>
> Singleton classes are beneficial because:
>
> - Removes the overhead of having multiple instances of the one object
> when there is no need
> - Allows you to keep the objects state rather than always starting =
from
> an initial state.
> - They provide namespaces with the benefits of polymorphism (eg -
> singleton classes can override / inherit from each other)
>
> Throughout this document, I will use an example of a singleton class
> "members" which acts as an interface to a database table.
> This class can save and load members from this database table simply =
by
> calling the following methods in this class.
>
> members::get($member_id) Loads a member from a member id and returns =
an
> associative array with info about that member
> members::save($member) Saves a member to the database from an array of
> properties about that member
>
> With the recent phase of tiered and service oriented architecture, the
> need for Singleton has become more and more apparent.
>
> ###
> # Singleton in php5
> ###
> In the past, I have implemented Singleton two different ways.  Both of
> these have problems.
>
> # Method 1:
> The first method involves having a public static getInstance method in
> every singleton class.  This sucks because you
> need to manually copy and paste it into every singleton class you =
make.
> Using a singleton class in this way is also confusing
> for novice programmers. Eg:
>
> <?php
>
> class members
> {
>         static public function getInstance()
>         {
>                 static $object =3D null;
>
>                 if($object)
>                 {
>                         return $object;
>                 }
>
>                 $object =3D new members();
>                 return $object;
>         }
>
>         /**
>          * Returns a member from the database based on their id
>          */
>         function get($id)
>         {
>                 // ...
>         }
>
>         // save method etc...
> }
>
> // Usage
> $arrMember =3D members::getInstance()->get(49);
> $arrMember['member_f_name'] =3D 'Scott';
> members::getInstance()->save($arrMember);
>
> ?>
>
> # Method 2:
> This method involves an associative array of class names to their
> instances, probably via a helper function similar to this.
>
> <?php
>
> class members
> {
>         /**
>          * Returns a member from the database based on their id
>          */
>         function get($id)
>         {
>                 // ...
>         }
>
>         // save method etc...
> }
>
> /**
>  * Returns an instance of a singleton class from its class name
>  */
> function getInstance($strClass)
> {
>         static $objects =3D array();
>
>         if(!isset($objects[$strClass]))
>         {
>                 return $objects[$strClass];
>         }
>
>         $objects[$strClass] =3D new members();
>         return $objects[$strClass];
> }
>
> // Usage
> $arrMember =3D getInstance('members')->get(49);
> $arrMember['member_f_name'] =3D 'Scott';
> getInstance('members')->save($arrMember);
>
> ?>
>
> This sucks because its slow, confusing for novices, and IDEs never =
pick
> up the class for code hinting.
>
> ###
> # Proposed new functionality
> ###
>
> I propose that singleton classes become a native part of the php
> language by adding the "singleton" class modifier T_SINGLETON.
>
> I don't know if native singleton classes have been implemented in a
> language before.  Most other languages eg - C++
> you can use template classes or generics to implement a clean
> singleton.
>
> The zend engine could feature a hash table and store the instances of
> objects.
>
> An example of the new way of using singleton classes would be:
>
> <?php
>
> /**
>  * A class for saving / retreiving members from a database
>  */
> singleton class members extends dataadapter
> {
>         /**
>          * Returns a member from the database based on their id
>          */
>         function get($id)
>         {
>                 // ...
>         }
>
>         // save method etc...
> }
>
> // Usage
> $arrMember =3D members->get(49);
> members->save($arrMember);
>
> ?>
>
> ###
> # Edge cases / got-cha's
> ###
> Some investigation will have to be performed as to how inheritence =
will
> work with singletons.
>
> Eg
> - Never have singleton abstract classes?
>
> - What happens when $members =3D new members() is called
> -- I say an exception being thrown and a suggestion to remove "new"
>
> - Is it ok to go $members =3D members; ?
> -- I'd say yes
>
> - Singleton constructors should not have parameters
>
> - Perhaps a new function singleton_getobjects needs to be added to
> enable access to the internal hash table
>
> - Dereferencing a non-singleton class should produce the same error
>
> --
> PHP Internals - PHP Runtime Development Mailing List
> To unsubscribe, visit: http://www.php.net/unsub.php
>
>


--=20
Guilherme Blanco - Web Developer
CBC - Certified Bindows Consultant
Cell Phone: +55 (16) 9166-6902
MSN: guilhermeblanco@hotmail.com
URL: http://blog.bisna.com
S=E3o Carlos - SP/Brazil