From: scott dot mcnaught at synergy8 dot com
Operating system: All
PHP version: 6CVS-2006-12-25 (CVS)
PHP Bug Type: Feature/Change Request
Bug description: Native Singleton Implementation
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 $object = null;
if($object)
{
return $object;
}
$object = new members();
return $object;
}
/**
* Returns a member from the database based on their id
*/
function get($id)
{
// ...
}
// save method etc...
}
// Usage
$arrMember = members::getInstance()->get(49);
$arrMember['member_f_name'] = 'Scott';
members::getInstance()->save($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 $objects = array();
if(!isset($objects[$strClass]))
{
return $objects[$strClass];
}
$objects[$strClass] = new members();
return $objects[$strClass];
}
// Usage
$arrMember = getInstance('members')->get(49);
$arrMember['member_f_name'] = 'Scott';
getInstance('members')->save($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
$arrMember = members->get(49);
members->save($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 = new members() is called
-- I say an exception being thrown and a suggestion to remove "new"
- Is it ok to go $members = 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
--
Edit bug report at http://bugs.php.net/?id=39946&edit=1
--
Try a CVS snapshot (PHP 4.4):
http://bugs.php.net/fix.php?id=39946&r=trysnapshot44
Try a CVS snapshot (PHP 5.2):
http://bugs.php.net/fix.php?id=39946&r=trysnapshot52
Try a CVS snapshot (PHP 6.0):
http://bugs.php.net/fix.php?id=39946&r=trysnapshot60
Fixed in CVS: http://bugs.php.net/fix.php?id=39946&r=fixedcvs
Fixed in release:
http://bugs.php.net/fix.php?id=39946&r=alreadyfixed
Need backtrace: http://bugs.php.net/fix.php?id=39946&r=needtrace
Need Reproduce Script: http://bugs.php.net/fix.php?id=39946&r=needscript
Try newer version: http://bugs.php.net/fix.php?id=39946&r=oldversion
Not developer issue: http://bugs.php.net/fix.php?id=39946&r=support
Expected behavior: http://bugs.php.net/fix.php?id=39946&r=notwrong
Not enough info:
http://bugs.php.net/fix.php?id=39946&r=notenoughinfo
Submitted twice:
http://bugs.php.net/fix.php?id=39946&r=submittedtwice
register_globals: http://bugs.php.net/fix.php?id=39946&r=globals
PHP 3 support discontinued: http://bugs.php.net/fix.php?id=39946&r=php3
Daylight Savings: http://bugs.php.net/fix.php?id=39946&r=dst
IIS Stability: http://bugs.php.net/fix.php?id=39946&r=isapi
Install GNU Sed: http://bugs.php.net/fix.php?id=39946&r=gnused
Floating point limitations: http://bugs.php.net/fix.php?id=39946&r=float
No Zend Extensions: http://bugs.php.net/fix.php?id=39946&r=nozend
MySQL Configuration Error: http://bugs.php.net/fix.php?id=39946&r=mysqlcfg
