VAR scoping using structures
ColdFusion
At this stage in the game of ColdFusion, it is common knowledge why you must var-scope all variables in your methods in order to protect your data. In case this is something new to you, say you set a variable named "myVar" in method A. Say you had a method B and in it you had another "myVar" with a different purpose. Unless you declare your variables like this: <cfset var myVar = "something" /> that data is shared between both methods and can be overwritten.
So typically when you have a method you var-scope all your private variables including queries or anything else like this:
One thing I have never been fond of is that once this is done there is effectively no visible difference in your code between variables that are var scoped and variables that aren't. For example, let's say I var-scope mVarA and don't var-scope myVarB. When I access them in the method they visibly appear to be in the same scope... like this:
Looking at this, there is no visible way to see which of those variables is var-scoped without looking at the top of your method to see what you have done. Plus, as you add variables to your methods, that var-scoping area will grow and you can have a large section of protected declarations. I have found a different way to approach this by var-scoping a structure named "private" at the top of my methods. Then in my code I can simply use <cfset private.myVar = "" />. For example, the code above would become:
By doing this, I no longer have to go var-scope each individual variable, plus the code becomes far more obvious as to which variables exist in that "private" scope.
So typically when you have a method you var-scope all your private variables including queries or anything else like this:
<cffunction name="a" output="false" returntype="void">
<cfset var myVar = "" />
<cfset var qQuery = "" />
<..... then all your code ...>
</cffunction>
One thing I have never been fond of is that once this is done there is effectively no visible difference in your code between variables that are var scoped and variables that aren't. For example, let's say I var-scope mVarA and don't var-scope myVarB. When I access them in the method they visibly appear to be in the same scope... like this:
<cffunction name="a" output="false" returntype="string">
<cfset var myVarA = "" />
<cfset myVarB = "" />
<cfreturn myVarA & myVarB />
</cffunction>
<cfset var myVarA = "" />
<cfset myVarB = "" />
<cfreturn myVarA & myVarB />
</cffunction>
Looking at this, there is no visible way to see which of those variables is var-scoped without looking at the top of your method to see what you have done. Plus, as you add variables to your methods, that var-scoping area will grow and you can have a large section of protected declarations. I have found a different way to approach this by var-scoping a structure named "private" at the top of my methods. Then in my code I can simply use <cfset private.myVar = "" />. For example, the code above would become:
<cffunction name="a" output="false" returntype="string">
<cfset var private = structnew() />
<cfset private.myVarA = "" />
<cfset myVarB = "" />
<cfreturn private.myVarA & myVarB />
</cffunction>
<cfset var private = structnew() />
<cfset private.myVarA = "" />
<cfset myVarB = "" />
<cfreturn private.myVarA & myVarB />
</cffunction>
By doing this, I no longer have to go var-scope each individual variable, plus the code becomes far more obvious as to which variables exist in that "private" scope.
Matt Williams said:
I like this idea. Do you think using var. for the structure would work? Such as,
cfset var var.qQuery = ""
cfset var var.qQuery = ""
Dave Shuck said:
Matt, I just tested it and it seems to work. I kind of expected this line to barf....
cfset var var = structnew()
... but it didn't!
I may have just changed my standard. :)
cfset var var = structnew()
... but it didn't!
I may have just changed my standard. :)
Dave Shuck said:
Matt, one other thing... I noticed in your comment you are re-var'ing it in your cfset. By var'ing the structure, you don't have to declare any other 'var's. You would just say:
cfquery name="var.myQuery"
...and it would already be in the var scope as an element of the var structure.
cfquery name="var.myQuery"
...and it would already be in the var scope as an element of the var structure.
Matt Williams said:
Gotcha. I meant what you said. I just tried the same and it worked for me to. In Eclipse, the var keyword is color coded even if it is part of the struct. So I'll have to decide if I like that or not. On one hand, it stands out and I really know what kind of variable it is. On the other hand, it could get confusing. Not to mention the intial 'cfset var var' looks like a typo.
Matt Williams said:
While stealing your array iterator code, I thought I'd post an update to this blog entry. I settled on
var vars=StructNew();
vars.myVar = "Foo";
Using var for the name of the structure was confusing me a bit. I've seen some other code using 'local' for the struct name.
Keep up the good work...
var vars=StructNew();
vars.myVar = "Foo";
Using var for the name of the structure was confusing me a bit. I've seen some other code using 'local' for the struct name.
Keep up the good work...
Dave Shuck said:
I like that approach. I have stuck with 'private' for no other reason than the fact that it is clear to me. But 'vars' is certainly equally clear. Regardless, I am still a fan of this approach in general and kind of surprised that it isn't more widely used.
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