Posted in ColdFusion | Posted on 11-25-2005 | 2,635 views
Nick asks:
Quick question: is there any difference between using <cfset variables.databasename = "" /> and <cfset var databasename = "" /> in a CFC?
It makes a big difference. A CFC, like a 'normal' CFM page, has a Variables scope. Inside a CFC, a variable in the Variables scope is accessible anywhere. So, as a typical example, one may use Variables.DSN throughout a CFC to retrieve a datasource variable. Here is some quick pseudo-code showing an example of setting the variable in the init() function then using it later. Again - this is pseudo-code and I haven't had a full cup of coffee yet:
2
3<cfset variables.dsn = "">
4
5<cffunction name="init">
6 <cfargument name="dsn" type="string" required="true">
7
8 <cfset variables.dsn = arguments.dsn>
9
10 <cfreturn this>
11</cffunction>
12
13<cffunction name="fixMyXBox">
14 <cfset var q = "">
15
16 <cfquery name="q" datasource="#variables.dsn#">
17 select .....
18 </cfquery>
19
20 <cfreturn q>
21</cffunction>
22
23</cfccmponent>
A var scope variable, however, only exists for the execution of the method. Look in my example above at the fixMyXBox method. That method creates one variable, a query, so I use the var scope to keep it local to the method itself. Once the method ends, q will no longer exist, but variables.dsn will stick around. (To be clear, it will stick around if you are calling more methods in the same instance of the CFC. But I think you get my point.)
Let me rewrite that. Just never, ever, leave the scope off of Variables values. Always specify it. The only unscoped vars should be local variables.
i use this var method like you preach, have since i got a preaching sometime ago, years maybe. anyway, when working with that method, or function i feel weird not having a "something." in front of it, like its an unscoped variable, and i could maybe duplicate names or something, it just feels odd. anyway, does this have a prefix?
later
sometimes in like spur of the moment game programming i might forget to, but i do not think there are any cases where i do not use a scoped variable, EVER, i find it in legacy code all the time, but i just fix and go on.
its funny to look back at old code and see instances of too many and WHOLLY not needed #'s all over the place.
anyway, ok, so im not the only one on this... nice.
I always use the 'variables' prefix to scope variables, even outside CFCs.
In CFCs methods (and UDFs), I always use local scoped variables when I don't need to retain the value.
I usually create a local scoped structure to hold them, e.g.:
<cfscript>
var local = structNew();
local.myVar1 = ...
local.myVar2 = ...
</cfscript>
That way you recognize local scoped variables very easily.
I borrowed this technique from a Fusebox sample application and it worked fine for me so far.
What do you think about it?
Thanks.
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