MACROMEDIA COLDFUSION MX 61-DEVELOPING COLDFUSION MX, Develop Manual

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88 Chapter 4: Using Expressions and Pound Signs
Function syntax
The following table shows function syntax and usage guidelines:
All functions return values. In the following example, the
cfset
tag sets a variable to the value
returned by the
Now
function:
<cfset myDate = DateFormat(Now(), "mmmm d, yyyy")>
You can use the values returned by functions directly to create more complex expressions, as in the
following example:
Abs(Myvar)/Round(3.14159)
For more information on how to insert functions in expressions, see “Using pound signs”
on page 89 .
Optional function arguments
Some functions take optional arguments after their required arguments. If omitted, all optional
arguments default to a predefined value. For example:
•
Replace("Eat and Eat", "Eat", "Drink")
returns "Drink and Eat"
•
Replace("Eat and Eat", "Eat", "Drink", "All")
returns "Drink and Drink"
The difference in the results is because the
Replace
function takes an optional fourth argument
that specifies the scope of replacement. The default value is “One,” which explains why only the
first occurrence of “Eat” was replaced with “Drink” in the first example. In the second example, a
fourth argument causes the function to replace all occurrences of “Eat” with “Drink”.
Expression evaluation and functions
It is important to remember that ColdFusion evaluates function attributes as expressions before it
executes the function. As a result, you can use any ColdFusion expression as a function attribute.
For example, consider the following lines:
<cfset firstVariable = "we all need">
<cfset myStringVar = UCase(firstVariable & " more sleep!")>
When ColdFusion server executes the second line, it does the following:
1
Determines that there is an expression with a string concatenation.
2
Evaluates the firstVariable variable as the string "we all need".
3
Concatenates "we all need" with the string " more sleep!" to get "we all need more sleep!".
4
Passes the string "we all need more sleep!" to the
UCase
function.
Usage Example
No arguments Function()
Basic format Function(Data)
Nested functions Function1(Function2(Data))
Multiple arguments Function(Data1, Data2, Data3)
String arguments Function('This is a demo')
Function("This is a demo")
Arguments that are expressions Function1(X*Y, Function2("Text"))