
Contents > Developing ColdFusion MX Applications > Writing and Calling User-Defined Functions > Creating user-defined functions > Rules for function definitions

Rules for function definitions

The following rules apply to functions that you define using CFScript or the cffunction tag:

The function name must be unique. It must be different from any existing variable, UDF, or built-in function name.
The function name must not start with the letters cf in any form. (For example, CF_MyFunction cfmyFunction, and cfxMyFunction are not valid UDF names.)
You cannot redefine or overload a function. If a function definition is active, ColdFusion generates an error if you define a second function with the same name.
You cannot nest function definitions; that is, you cannot define one function inside another function definition.
The function can be recursive, that is, the function definition body can call the function.
The function does not have to return a value.

You can define a function in the following places:

On the page where it is called. You can even define it below the place on the page where it is called, but this poor coding practice can result in confusing code.
On a page that you include using a cfinclude tag. The cfinclude tag must be executed before the function gets called. For example, you can define all your application's functions on a single page and place a cfinclude tag at the top of pages that use the functions.
On any page that puts the function name in a scope common with the page on which you call the function.
On the Application.cfm page.

For recommendations on selecting where you define functions, see the sections Using Application.cfm and function include files and Specifying the scope of a function.


Contents > Developing ColdFusion MX Applications > Writing and Calling User-Defined Functions > Creating user-defined functions > Rules for function definitions

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