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Posted by Jerry Stuckle on 11/16/07 02:27
Rob Wilkerson wrote:
> On Nov 14, 6:33 pm, Michael Fesser <neti...@gmx.de> wrote:
>> .oO(Rob Wilkerson)
>>
>>> I suppose I just don't understand the concept of "globally
>>> available from everywhere in your scripts" if a "new" instance is
>>> actually being created with each request.
>> OK. I just meant that you can easily access the singleton from within
>> every other function or method in your currently running script:
>>
>> function foo() {
>> $obj = TMyClass::getInstance();
>> $obj->doSomething();
>>
>> }
>>
>> Wherever you need the singleton, you just have to call the getInstance()
>> method. It's like the 'global' keyword for importing global variables
>> into the local scope, but IMHO cleaner and more flexible. Of course the
>> next HTTP request is an entirely different thing and starts it all over
>> again.
>
> I guess what I keep coming back to is that this seems to have limited
> practical use as a singleton. True, its instantiation becomes global
> despite the fact that it may was instantiated (in your example) within
> a traditionally scoped element (a function), but that seems like a
> minor - and almost accidental - benefit. I don't tend to use
> standalone functions that have no context, so scoping issues don't
> really come up.
>
> Additionally, my working practice is to use dependency injection
> rather than create objects "on demand". That gives me a certain level
> of controlled immutability. And, since the length of a request is so
> short, it's usually pretty easy to feel reasonably secure that, during
> the life of that request, an object instantiated in the "normal"
> manner hasn't mutated to any kind of unusable (or unexpected) state
> (perhaps I'm just naive?).
>
> Anyway, I'm not trying to be difficult. Just trying to understand how
> to best use singletons in a PHP context, their capabilities and their
> limitations. You all have been a lot of help and I appreciate it.
>
I use them all the time. For instance, I might have a database class.
I might have several business classes which access tables in the
database. Each business class operates independently of the other
classes; I may use one or several in any once page.
The singleton class for the database means each of the business classes
can get the one instance of the database class. If the database object
doesn't exist, it is created and returned. If it does exist, it is just
returned.
Saves from having multiple connections to the database unnecessarily yet
business classes don't need each create their own classes, and the main
page code doesn't worry at all about the database.
--
==================
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attglobal.net
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