--- [EMAIL PROTECTED] wrote:
> Thanks Peter.
>
> I agree with everything except the use of the keyword "new". I think that
> it's just simply too confusing. People won't know whether they are getting
> a fresh instance or not.
>
> The "only" keyword suggestion is not bad. I think id prefer "get" or
> something. (or better no keyword at all ;))
Really it's best to stick with 'new' because of compatibility with
non-singletons:
$class = '...';
$a = new $class;
If you use a different keyword or syntax for singletons:
$class = '...';
$a = is_singleton($class)
? singleton $class
: new $class;
And you would end up reproducing that anywhere you have to create an instance
of an unknown class.
> Do you see this as being a useful feature?
There's plenty of room to improve PHP's OO capabilities for PHP6, and
singletons are a good start.
regards,
Peter
> Scott
>
>
> -----Original Message-----
> From: Peter Hodge [mailto:[EMAIL PROTECTED]
> Sent: Tuesday, 6 March 2007 3:55 PM
> To: [EMAIL PROTECTED]; 'Guilherme Blanco'
> Cc: internals@lists.php.net
> Subject: RE: [PHP-DEV] Native Singleton Implementation
>
> Also posted in the bug report:
>
>
>
> Perhaps some nicer solutions to your got-cha's:
>
> - What happens when $members = new members() is called
>
> If the class is defined as a singleton, then PHP should create the
> instance as
> normal (this includes calling __construct() ) and store it in the hash
> table,
> or return the cached instance if it's already created.
>
> -- I say an exception being thrown and a suggestion to remove "new"
>
> You should still be able to use 'new', with the expectation that if the
> class
> is a singleton, you might actually get a cached instance, rather than a
> 'new'
> instance, but it's not very difficult to understand:
>
> $a = new members;
> $b = new members;
> $c = new members;
> // $a $b and $c are all the same instance because members is a singleton
>
> If you really think 'new' is too ambiguous, why not add a new token such as
> 'only', which is used for instantiation of singletons?
>
> $a = only members;
> $b = only members;
> $c = only members;
> // it's a bit more obvious $a $b and $c are the same instance.
>
> - Is it ok to go $members = members; ?
>
> That's too ambiguous. In that example 'members' could be a constant,
> singleton, or simply the string 'members'.
>
> - Singleton constructors should not have parameters
>
> Perhaps they could (and it might be useful), if it's done like this:
>
> $a = new members(1, 2, 3); // arguments are passed to __construct()
> $b = new members(3, 2, 1); // arguments are ignored, object has already
> been
> constructed
> $c = new members(4, 5, 6); // arguments are ignored, object has already
> been
> constructed
>
> - Perhaps a new function singleton_getobjects needs to be added to enable
> access to the internal hash table
>
> Not a bad idea. Getting in 'through the back door' is really important. Why
> not also a 'singleton_is_loaded()', and an 'is_singleton()'? Obviously this
> would eventually need to be visible through the Reflection classes (etc,
> etc).
>
> - Never have singleton abstract classes?
>
> I think that would be an unfair limitation.
>
>
>
> 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().
>
>
> regards,
> Peter
>
>
>
>
>
>
> --- [EMAIL PROTECTED] wrote:
>
> > 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 dont 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 dont 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=39946) and they
> > both have drawbacks.
> >
> > Hmm... give the bug report a quick read over again :)
> >
> >
> > -----Original Message-----
> > From: Guilherme Blanco [mailto:[EMAIL PROTECTED]
> > Sent: Monday, 5 March 2007 6:21 AM
> > To: [EMAIL PROTECTED]
> > 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, [EMAIL PROTECTED] <[EMAIL PROTECTED]>
> 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=39946
> > >
> > > 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 $object = null;
> > >
> > > if($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
> > >
> > > --
> > > PHP Internals - PHP Runtime Development Mailing List
> > > To unsubscribe, visit: http://www.php.net/unsub.php
> > >
> > >
> >
> >
> > --
> > Guilherme Blanco - Web Developer
> > CBC - Certified Bindows Consultant
> > Cell Phone: +55 (16) 9166-6902
> > MSN: [EMAIL PROTECTED]
> > URL: http://blog.bisna.com
> > São Carlos - SP/Brazil
> >
> > --
> > PHP Internals - PHP Runtime Development Mailing List
> > To unsubscribe, visit: http://www.php.net/unsub.php
> >
> >
>
>
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