For index loops in ColdFusion that are looping over an array or list, I always put the ArrayLen() or ListLen() in the TO attribute. I always felt a little uneasy about it because I thought maybe the function was getting evaluated for each iteration of the index loop. My fear was that this was adding additional processing overhead for each iteration.

Well, I finally got my out of shape butt off the proverbial couch and actually tested what was going on:

  • <cfoutput>
  •  
  • <!--- Create an initial array of items. --->
  • <cfset arrItems = ListToArray( "ben,dave,mark,mike" ) />
  •  
  • Original Length: #ArrayLen( arrItems )#<br />
  • <br />
  •  
  • <!---
  • Loop over the items in the array. For each iteration, add
  • an item to the array to see if the loop will keep going.
  • In the TO attribute, use the Min() method to ensure that
  • the loop doesn't go on infinitely.
  • --->
  • <cfloop
  • index="intIndex"
  • from="1"
  • to="#Min( 10, ArrayLen( arrItems) )#"
  • step="1">
  •  
  • <!--- Output the iteration values. --->
  • Iteration #intIndex#. Array Length: #ArrayLen( arrItems )#<br />
  •  
  • <!--- Add an Item to the array to see if we keep looping. --->
  • <cfset ArrayAppend(
  • arrItems,
  • "sarah"
  • ) />
  •  
  • </cfloop>
  •  
  • </cfoutput>

Turns out, the loop only iterates 4 times; the attributes only get evaluated that first time. When you stop to think about it, that makes a lot of sense; it is just a string. And if you take Conditional loops into account, it makes sense that the condition="" attribute is a string, not an evaluation. That way it can do a sort of delayed evaluation on the condition.

Man, understanding the basics is so important.