76
DEVELOPING
COLDFUSION 9 APPLICATIONS
The CFML Programming Language
Las
t
upda
te
d 8/5/2010
The following example shows the
Evaluate
function and how it works with ColdFusion variable processing:
<cfset myVar2="myVar">
<cfset myVar="27/9">
<cfoutput>
#myVar2#<br>
#myVar#<br>
#Evaluate("myVar2")#<br>
#Evaluate("myVar")#<br>
#Evaluate(myVar2)#<br>
#Evaluate(myVar)#<br>
</cfoutput>
Reviewing the code
The following table describes how ColdFusion processes this code:
As you can see, using dynamic expressions can result in substantial expression evaluation overhead, and the code can
be confusing. Therefore, you should avoid using dynamic expressions wherever a simpler technique, such as using
indexed arrays or structures can serve your purposes.
Avoiding the Evaluate function
Using the
Evaluate
function increases processing overhead, and in most cases it is not necessary. These examples
show some cases where you can consider using the
Evaluate
function:
Code
Description
<cfset myVar2="myVar">
<cfset myVar="27/9">
Sets the two variables to the following strings:
myVar
27/9
<cfoutput>
#myVar2#<br/>
#myVar#<br/>
Displays the values assigned to the variables, myVar and 27/9, respectively.
#Evaluate("myVar2")#<br>
Passes the string "myvar2" (without the quotation marks) to the Evaluate function, which
does the following:
1
Evaluates it as the variable myVar2.
2
Returns the value of the myVar2 variable, the string "myvar" (without the quotation
marks).
#Evaluate("myVar")#<br>
Passes the string "myvar" (without the quotation marks) to the Evaluate function, which
does the following:
1
Evaluates it as the variable myVar.
2
Returns the value of the myVar variable, the string "27/9" (without the quotation marks).
#Evaluate(myVar2)#<br>
Evaluates the variable myVar2 as the string "myVar" and passes the string (without the
quotation marks) to the Evaluate function. The rest of the processing is the same as in the
previous line.
#Evaluate(myVar)#<br/>
</cfoutput>
Evaluates the variable myVar as the string "27/9" (without the quotation marks), and passes
it to the Evaluate function, which does the following:
1
Evaluates the string as the expression 27/9
2
Performs the division.
3
Returns the resulting value, 3