MACROMEDIA COLDFUSION MX 61-DEVELOPING COLDFUSION MX, Develop Manual, Page: 202 / 860

202 Chapter 10: Writing and Calling User-Defined Functions
Using a CFML tag in a user-defined function
The most important advantage of using the
cffunction
tag over defining a function in CFScript
is that you can include CFML tags in the function. Thus, UDFs can encapsulate activities, such
as database lookups, that require ColdFusion tags. Also, you can use the
cfoutput
tag to display
output on the calling page with minimal coding.
Tip: To improve performance, avoid using the
cfparam
tag in ColdFusion functions. Instead, use the
cfset
tag.
The following example function looks up and returns an employee’s department ID. It takes one
argument, the employee ID, and looks up the corresponding department ID in the CompanyInfo
Employee table:
<cffunction name="getDeptID" >
<cfargument name="empID" required="true" type="numeric">
<cfquery dataSource="CompanyInfo" name="deptID">
SELECT Dept_ID
FROM Employee
WHERE Emp_ID = #empID#
</cfquery>
<cfreturn deptID.Dept_ID>
</cffunction>
Using the Arguments scope in cffunction definitions
When you define a function using the
cffunction
tag, you generally refer to the arguments
directly by name if all arguments are named in the
cfargument
tags. If you do use the Arguments
scope identifier, follow the rules listed in “About the Arguments scope” on page 194 .
Calling functions and using variables
You can call a function anywhere that you can use an expression, including in pound signs (#) in
a
cfoutput
tag, in a CFScript, or in a tag attribute value. One function can call another function,
and you can use a function as an argument to another function.
You call user-defined functions the same way you call any built-in ColdFusion functions.
Passing arguments
ColdFusion passes the following data types to the function by value:
•
Integers
•
Real numbers
•
Strings (including lists)
•
Date-time objects
•
Arrays
As a result, any changes that you make in the function to these arguments do not affect the
variable that was used to call the function, even if the calling code is on the same ColdFusion page
as the function definition.
ColdFusion passes queries, structures, and external objects such as COM objects into the
function by reference. As a result, any changes to these arguments in the function also change the
value of the variable in the calling code.
For an example of the effects of passing arguments, see “Passing complex data” on page 210 .