Using the Evaluate function increases processing overhead, and in most cases it is not necessary. The following sections provide examples of cases where you might consider using the Evaluate function.
You might be inclined to use the Evaluate function in code such as the following:
<cfoutput>1 + 1 is #Evaluate(1 + 1)#</cfoutput>
Although this code works, it is not as efficient as the following code:
<cfset Result = 1 + 1> <cfoutput>1 + 1 is #Result#</cfoutput>
This example shows how you can use an associative array reference in place of an Evaluate function. This technique is powerful because:
The following example uses the Evaluate function to construct a variable name:
<cfoutput> Product Name: #Evaluate("Form.product_#i#")# </cfoutput>
This code comes from an example where a form has entries for an indeterminate number of items in a shopping cart. For each item in the shopping cart there is a product name field. The field name is of the form product_1, product_2, and so on, where the number corresponds to the product's entry in the shopping cart. In this example, ColdFusion does the following:
The following example has the same result as the preceding example and is more efficient:
<cfoutput> ProductName: #Form["product_" & i]# </cfoutput>
In this code, ColdFusion does the following:
This code format does not use any dynamic evaluation, but it achieves the same effect, of dynamically creating a structure reference by using a string and a variable.