
Contents > Developing ColdFusion MX Applications > Using Expressions and Pound Signs > Dynamic expressions and dynamic variables > About dynamic expressions and dynamic evaluation Selecting how to create variable names

Selecting how to create variable names

The following two examples describes cases when you need dynamic variable names:

Form applications where the number and names of fields on the form vary dynamically. In this case, the form posts only the names and values of its fields to the action page. The action page does not know all the names of the fields, although it does know how the field names (that is, the variable names) are constructed.
If the following are true:
- ColdFusion calls a custom tag multiple times.
- The custom tag result must be returned to different variables each time.
- The calling code can specify the variable in which to return the custom tag result.
In this case, the custom tag does not know the return variable name in advance, and gets it as an attribute value.

In both cases, it might appear that dynamic expressions using the Evaluate function are needed to construct the variable names. However, you can achieve the same ends more efficiently by using dynamic variable naming, as shown in Example: a dynamic shopping cart.

This does not mean that you must always avoid dynamic evaluation. However, given the substantial performance costs of dynamic evaluation, you should first ensure that one of the following techniques cannot serve your purpose:

An array (using index variables)
Associative array references containing expressions to access structure elements
Dynamically generated variable names


Contents > Developing ColdFusion MX Applications > Using Expressions and Pound Signs > Dynamic expressions and dynamic variables > About dynamic expressions and dynamic evaluation Selecting how to create variable names

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imstillatwork said on Nov 19, 2005 at 5:09 PM :

For example, you should reference form variables as the structure that they are when you are dynamically creating an unknown number of input fields.

#form["name_" & i]#

rather then building a string and using evaluate...

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