While fixing my cfTrigger framework recently, I realized that I have messed up the scopes of variables inside cfcs seriously! I omitted the var keyword for local variables and used This keyword where it should have been Variables. So before continuing to fix it, I decided to take a step back and learn again in a more proper way what variable scopes are available in Coldfusion cfcs and how to use them correctly.

There are many scopes for variables in Coldfusion such as Application, session, form, url, public, private, etc. but in this article I am only interested in the scopes related to cfcs. These include the This scope variables, Variables scope variables, variables defined with the var keyword and those defined without any keyword or scope. Keep in mind that these are considered inside a cfc context.

Findings Summary

Below is the summary of Coldfusion variable scopes related to cfcs:

Declare with	Example	Scope	Notes
This	<cfset This.name = "khoa">	Public	Available throughout the entire cfc and also to the caller
Variables	<cfset Variables.name = "khoa">	Private to the cfc	Available throughout the entire cfc but not to the caller
Var	<cfset var name = "khoa">	Private to the function	Available to the function where the declaration appears, not available to any other functions inside the cfc or the caller
[NOTHING]	<cfset name = "khoa">	Same as Variables	This is essentially the same as using the Variables scope. So it's better to explicitly write the Variables scope to avoid confusion

Example

Due to the example file being a little bit long, I won't post it here. But please download them at the end of this article to test them out yourself. In the example, I have a Person class (person.cfc) that has a number of local variables, VARIABLES (cfc) variables, THIS variables and some declared without any scope or keyword. I then use a cfm file to display them to show you which ones are available at which scopes. Download and open the files and read on to see my explanation of the example.

What I did in the example:

1. Call a function to display the Variables scope variables from inside the object. This returns:

   • Variables that are defined with the explicit Variables scope, and
   • Variables that are defined without using any scope

   This happens regardless of where the variables are defined: in the same function, in another function or at the top of the cfc outside all functions.

   

2. Call a function to display the This scope variables from inside the object. This returns:

   • Variables that are defined with the explicit This scope

   Again, this happens regardless of where the variables are defined.

   

3. Display the list of variables available to the caller from outside the object. This returns:

   • Variables that are defined with the explicit This scope

   This is the same list of variables as in the second call above.

   

Notes: I only display the simple values in this example. If you dump the Variables or This scope, you will have much more such as other variable types and function definitions.

Takeaways

• Always declare local variables with the var keyword, or you will (very likely) receive unexpected results
• Use VARIABLES scope to store variables that you want to be shared, available, across the entire cfc. This is especially useful in the init method, where you initialize the object and would like to store some object properties for later use.
• Use scope (or the var keyword) when declaring variables inside cfc to keep them organized and avoid variables appearing where you don't expect them. Without a scope, it will default to the VARIABLES scope. So it's always good to explicitly give it a scope.
• In Coldfusion, This is public while it is generally private in most other languages. And as in any other languages, try to limit the number of public variables. Only expose as much as you need to. That means limit the use of This.

Download example

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