Question

I would like to test:

<cfif Exists(MyStruct['mittens'])> </cfif> 

If the ‘mittens’ key doesn’t exist in MyStruct, what will it return? 0, or ”??

What should replace Exists function?

UPDATE

I tried,

<cfif IsDefined(MyStruct.mittens)> 

Which also throws the error

Element Mittens is undefined in MyStruct.

Answer 1

To test for key existence, I recommend:

<cfif StructKeyExists(MyStruct, 'mittens')>  <!--- or --->  <cfset key = 'mittens'> <cfif StructKeyExists(MyStruct, key)> 

Behind the scenes this calls the containsKey() method of the java.util.map the ColdFusion struct is based on. This is arguably the fastest method of finding out if a key exists.

The alternative is:

<cfif IsDefined('MyStruct.mittens')>  <!--- or --->  <cfset key = 'mittens'> <cfif IsDefined('MyStruct.#key#')> 

Behind the scenes this calls Eval() on the passed string (or so I believe) and tells you if the result is a variable reference. In comparison this is slower than StructKeyExists(). On the plus side: You can test for a sub-key in a nested structure in one call:

<cfif IsDefined('MyStruct.with.some.deeply.nested.key')>