factory pattern in php

[Michael G]

I want to use a factory pattern to create a variety of objects. Which object
gets created depends on a string that is passed to the factory create
method. I would like to avoid using an if or switch construct to accomplish
this but not sure how. For example,

....

if($nextObject == "login")
{
return new Login();
}
else if($nextObject == "validateda ta")
{
return new Validate(aStrin g);
}

....
Is there any way to avoid this?

Thanks, Mike



----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

[Michael G]

Re: factory pattern in php


"Michael G" <mike-g@montana.com> wrote in message
news:42e66b59$1 _2@spool9-west.superfeed. net...[color=blue]
>I want to use a factory pattern to create a variety of objects. Which
>object gets created depends on a string that is passed to the factory
>create method. I would like to avoid using an if or switch construct to
>accomplish this but not sure how. For example,
>
> ...
>
> if($nextObject == "login")
> {
> return new Login();
> }
> else if($nextObject == "validateda ta")
> {
> return new Validate(aStrin g);
> }
>
> ...
> Is there any way to avoid this?
>[/color]


Actually there is a way to do this but I am sure how appropriate it is.
Here is a simple of example of the concept. It does what I want but not
convinced this is the best way to do it. If it is then I could simply place
a list of strings in an array and index them with an input string.

<?php

class A
{
function A()
{
print("creating A");
}

}


$a = "A";
new $a."()";

?>

Thanks mike



----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

[Jacob Atzen]

Re: factory pattern in php

On 2005-07-26, Michael G <mike-g@montana.com> wrote:[color=blue]
> I want to use a factory pattern to create a variety of objects. Which object
> gets created depends on a string that is passed to the factory create
> method. I would like to avoid using an if or switch construct to accomplish
> this but not sure how. For example,
>
> ...
>
> if($nextObject == "login")
> {
> return new Login();
> }
> else if($nextObject == "validateda ta")
> {
> return new Validate(aStrin g);
> }
>
> ...
> Is there any way to avoid this?[/color]

You could do:

function create($classNa me) {
return new $className;
}

Not sure if it's a better solution though.

--
Cheers,
- Jacob Atzen

[Michael G]

Re: factory pattern in php


"Jacob Atzen" <jacob@aub.dk > wrote in message
news:slrndecvlr .a1s.jacob@tank .aub.dk...[color=blue]
> On 2005-07-26, Michael G <mike-g@montana.com> wrote:[color=green]
>> I want to use a factory pattern to create a variety of objects. Which
>> object
>> gets created depends on a string that is passed to the factory create
>> method. I would like to avoid using an if or switch construct to
>> accomplish
>> this but not sure how. For example,
>>
>> ...
>>
>> if($nextObject == "login")
>> {
>> return new Login();
>> }
>> else if($nextObject == "validateda ta")
>> {
>> return new Validate(aStrin g);
>> }
>>
>> ...
>> Is there any way to avoid this?[/color]
>
> You could do:
>
> function create($classNa me) {
> return new $className;
> }
>
> Not sure if it's a better solution though.
>[/color]

That's not a bad idea. It would eliminate the need for an array of strings.

Thanks, Mike



----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

[Michael G]

Re: factory pattern in php


"Michael G" <mike-g@montana.com> wrote in message
news:42e6a0f3$1 _1@spool9-west.superfeed. net...[color=blue]
>
> "Jacob Atzen" <jacob@aub.dk > wrote in message
> news:slrndecvlr .a1s.jacob@tank .aub.dk...[color=green]
>> On 2005-07-26, Michael G <mike-g@montana.com> wrote:[color=darkred]
>>> I want to use a factory pattern to create a variety of objects. Which
>>> object
>>> gets created depends on a string that is passed to the factory create
>>> method. I would like to avoid using an if or switch construct to
>>> accomplish
>>> this but not sure how. For example,
>>>
>>> ...
>>>
>>> if($nextObject == "login")
>>> {
>>> return new Login();
>>> }
>>> else if($nextObject == "validateda ta")
>>> {
>>> return new Validate(aStrin g);
>>> }
>>>
>>> ...
>>> Is there any way to avoid this?[/color]
>>
>> You could do:
>>
>> function create($classNa me) {
>> return new $className;
>> }
>>
>> Not sure if it's a better solution though.
>>[/color]
>
> That's not a bad idea. It would eliminate the need for an array of
> strings.[/color]

Just a note, some languages would not allow that. That makes me a bit
uncomfortable. They would require an explicit open/closed paran at a
minimum.

Mike



----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

[Andy Hassall]

Re: factory pattern in php

On Tue, 26 Jul 2005 14:43:36 -0600, "Michael G" <mike-g@montana.com> wrote:
[color=blue][color=green][color=darkred]
>>> function create($classNa me) {
>>> return new $className;
>>> }
>>>
>>> Not sure if it's a better solution though.
>>>[/color]
>>
>> That's not a bad idea. It would eliminate the need for an array of
>> strings.[/color]
>
>Just a note, some languages would not allow that. That makes me a bit
>uncomfortabl e. They would require an explicit open/closed paran at a
>minimum.[/color]

But you're not writing in other languages, you're writing in PHP where it's
valid syntax, so where's the problem?

--
Andy Hassall / <andy@andyh.co. uk> / <http://www.andyh.co.uk >
<http://www.andyhsoftwa re.co.uk/space> Space: disk usage analysis tool

[Michael G]

Re: factory pattern in php


"Andy Hassall" <andy@andyh.co. uk> wrote in message
news:jvbde11ijf rgk5rmjkp5mb9d6 k2evg1n80@4ax.c om...[color=blue]
> On Tue, 26 Jul 2005 14:43:36 -0600, "Michael G" <mike-g@montana.com>
> wrote:
>[color=green][color=darkred]
>>>> function create($classNa me) {
>>>> return new $className;
>>>> }
>>>>
>>>> Not sure if it's a better solution though.
>>>>
>>>
>>> That's not a bad idea. It would eliminate the need for an array of
>>> strings.[/color]
>>
>>Just a note, some languages would not allow that. That makes me a bit
>>uncomfortable . They would require an explicit open/closed paran at a
>>minimum.[/color]
>
> But you're not writing in other languages, you're writing in PHP where
> it's
> valid syntax, so where's the problem?
>[/color]

Between my ears!!

Just because the php interpreter doesn't barf doesn't necessarliy mean that
it is defined behavior. I have ran across this before with different
implementations of compilers, undefined behavior that is.

Thanks, Mike



----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

[Andy Hassall]

Re: factory pattern in php

On Tue, 26 Jul 2005 16:03:28 -0600, "Michael G" <mike-g@montana.com> wrote:
[color=blue][color=green]
>> But you're not writing in other languages, you're writing in PHP where
>> it's
>> valid syntax, so where's the problem?[/color]
>
>Between my ears!!
>
>Just because the php interpreter doesn't barf doesn't necessarliy mean that
>it is defined behavior. I have ran across this before with different
>implementation s of compilers, undefined behavior that is.[/color]

It's valid in Perl, and PHP's roots are in Perl :-)

The Objects page in the manual has an example of creating an object with just:

$cart = new Cart;

... no parens.

The definition of new (T_NEW) in Zend/zend_language_p arser.y:425 (in PHP
4.4.0's source) looks to me like it accepts a variable - so "new $className" is
fine.

--
Andy Hassall / <andy@andyh.co. uk> / <http://www.andyh.co.uk >
<http://www.andyhsoftwa re.co.uk/space> Space: disk usage analysis tool

[Michael G]

Re: factory pattern in php


"Andy Hassall" <andy@andyh.co. uk> wrote in message
news:g0dde11uu4 j8d9jrgdh1onv5v t8dj8raf3@4ax.c om...[color=blue]
> On Tue, 26 Jul 2005 16:03:28 -0600, "Michael G" <mike-g@montana.com>
> wrote:
>[color=green][color=darkred]
>>> But you're not writing in other languages, you're writing in PHP where
>>> it's
>>> valid syntax, so where's the problem?[/color]
>>
>>Between my ears!!
>>
>>Just because the php interpreter doesn't barf doesn't necessarliy mean
>>that
>>it is defined behavior. I have ran across this before with different
>>implementatio ns of compilers, undefined behavior that is.[/color]
>
> It's valid in Perl, and PHP's roots are in Perl :-)
>
> The Objects page in the manual has an example of creating an object with
> just:
>
> $cart = new Cart;
>
> ... no parens.
>
> The definition of new (T_NEW) in Zend/zend_language_p arser.y:425 (in PHP
> 4.4.0's source) looks to me like it accepts a variable - so "new
> $className" is
> fine.[/color]


ok. thanks. but if you start trying to add parameters using concatenation
then the interpreter doesn't like that.

for example:

new $a."(".$paren." )" //this does not work

Mike



----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

[Michael G]

Re: factory pattern in php


"Michael G" <mike-g@montana.com> wrote in message
news:42e6bfdb$1 _2@spool9-west.superfeed. net...[color=blue]
> new $a."(".$paren." )" //this does not work
>[/color]

this does work:

new $a($paren);

That seems so non-intuitive to me. Anyway, just not used to using a language
like this. I must say being able to use variables in this way really
increases the flexibility of the language. Not that a person needs to use
syntax like this alot but at least it is available.

On another note, since constructors are simply functions with the same name
as the enclosing class, a typical function could be called like this:

$a = "foo";

$a();

The result is very similar to using pointers to functions.

Mike




----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

[Justin Koivisto]

Re: factory pattern in php

Michael G wrote:
[color=blue]
> "Michael G" <mike-g@montana.com> wrote in message
> news:42e6a0f3$1 _1@spool9-west.superfeed. net...
>[color=green]
>>"Jacob Atzen" <jacob@aub.dk > wrote in message
>>news:slrndecv lr.a1s.jacob@ta nk.aub.dk...
>>[color=darkred]
>>>On 2005-07-26, Michael G <mike-g@montana.com> wrote:
>>>
>>>>I want to use a factory pattern to create a variety of objects. Which
>>>>object
>>>>gets created depends on a string that is passed to the factory create
>>>>method. I would like to avoid using an if or switch construct to
>>>>accomplis h
>>>>this but not sure how. For example,
>>>>
>>>>...
>>>>
>>>>if($nextObj ect == "login")
>>>>{
>>>> return new Login();
>>>>}
>>>>else if($nextObject == "validateda ta")
>>>>{
>>>> return new Validate(aStrin g);
>>>>}
>>>>
>>>>...
>>>>Is there any way to avoid this?
>>>
>>>You could do:
>>>
>>>function create($classNa me) {
>>> return new $className;
>>>}
>>>
>>>Not sure if it's a better solution though.
>>>[/color]
>>
>>That's not a bad idea. It would eliminate the need for an array of
>>strings.[/color]
>
> Just a note, some languages would not allow that. That makes me a bit
> uncomfortable. They would require an explicit open/closed paran at a
> minimum.[/color]

This is what you be considered a variable function. Best practice is to
include the parenthesis like:

$className='myC lass';
$a = new $className();

--
Justin Koivisto, ZCE - justin@koivi.co m

http://koivi.com

[Jacob Atzen]

Re: factory pattern in php

On 2005-07-27, Justin Koivisto <justin@koivi.c om> wrote:[color=blue]
> This is what you be considered a variable function. Best practice is to
> include the parenthesis like:[/color]

Why is this best practice? I can't seem to conjure any argument as to
why this should be better.

--
Cheers,
- Jacob Atzen