From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf
Of Barney Boisvert
Sent: Friday, October 14, 2005 6:29 PM
To: [email protected]
Subject: Re: [CFCDev] Inside the CFC: use Getter/Setter or Instance Scope
On 10/14/05, Phillip Senn <[EMAIL PROTECTED]> wrote:
> Here's what I've learned so far:
> 1.
> <cfset Variables.Counter... in CF is like
> DIM Counter as Variant in VB, declaring a local variable.
> <cfset This.Counter... in CF is like
> PUBLIC Counter as Variant in VB, declaring a global variable.
I don't know VB, but that sounds right. 'this' scope is available
inside and outside a CFC instance, 'variables' scope is only available
inside.
> 2.
> Putting all your variables into a structure is a good idea for
housekeeping
> purposes, but to call your structure "instance" is intellectually
dishonest.
> I don't believe you are instantiating an object, and calling your
structure
> "instance" tells me that you'd like for it to be an object, but really
> you're just mimicking OOP.
You can absolutely instantiate a CFC, and it becomes an instance of
that CFC. But calling it 'instance' is just convention. I happen to
call mine 'my' instead. As long as you're consistent it doesn't
really matter, but using conventions can make porting code and/or
developers easier.
The point is that CF's nested-struct nomeclature allows a very easy
way to differentiate between instance state and transient data it
might also need to store. In Java (and probably most other
languages), you have to use naming conventions, but with CF's structs,
you can package the variables together, and then act on the
separately, which is very useful in certain situations.
> Admittedly, I don't understand OOP so I shouldn't be criticizing, but
> calling a variable "Instance" confused me, even though I knew it was only
an
> example.
>
> OK, now that I've offended some people, let me show you my humble offering
> and let you tear it to shreds like Ray Camden would do if I were to submit
a
> "guess the number" page:
>
> The file "mycomponent.cfc" contains:
> <cfcomponent>
> <cfset Variables.Counter = 0>
Is this instance state, or is it some transient instance variable?
Named like this, it should be the latter. And why isn't it in the
(undeclared) init method? It ought to be.
> <cffunction name="getAge" access="public" returntype="string"
> displayname="Get a person's age" hint="Plugh">
> <cfargument name="BirthDate" type="date" required="yes">
> <cfargument name="CurrentDate" type="date" default="#NOW()#">
> <cfset Variables.Counter = Variables.Counter + 1>
Uh-oh, you're using your transient state in a way that makes me thing
that it's not really transient. You sure this shouldn't be
variables.instance.counter.
> <cfset Variables.Age = #DateDiff('yyyy',BirthDate,CurrentDate)#>
Same thing here. I'm assuming this is a transient variable? If it
is, then it should be a function-local variable (declared with 'var'),
and not in the variables scope at all.
> <cfreturn Variables.Age>
> </cffunction>
> </cfcomponent>
>
> The file "myPage.cfm" contains:
> <cfobject name="myObject" component="Components.mycomponent">
You're not calling the (undeclared) init method of your component to
initialize it.
> <cfset myBirthDate = CREATEODBCDATE('1/1/1900')>
> <cfset myAge= myObject.getAge(myBirthDate)>
> <cfoutput>#myAge#</cfoutput>
>
>
>
> Variables.Counter isn't necessary, but I threw it in there to illustrate
the
> way you would DIM a variable at the top of a VB module to make it
accessible
> to the entire module, or in this case, all the functions within the
> component.
>
> How'd I do?
Less important, but you don't have output="false" on your CFCOMPONENT
and CFFUNCTION tags, which you should always have. You can get some
weird spacing issues if you don't.
cheers,
barneyb
--
Barney Boisvert
[EMAIL PROTECTED]
360.319.6145
http://www.barneyb.com/
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