Functions returning TRUE or FALSE

What dou you think of the following version of your code? It is the same as your original code but, in my opinion, a bit simpler.  For example, your test now becomes something like

<!--- remember returntype is now a struct --->
<cfif convertDateToUTS(FORM.date).isConverted>
     <cfset date = convertDateToUTS(FORM.date).unixDateTime/>
     <p>Your date: <cfoutput>#date#</cfoutput></p>
<cfelse>
     <p>Could not convert date.</p>
      Reason: <cfoutput>#convertDateToUTS(FORM.date).message#</cfoutput>
</cfif>

<cffunction name="convertDateToUTS" output="no" returntype="struct">
    <cfargument name="date" required="Yes" />
    <cfargument name="time" default="00:00"/>
    <cfset var returnStruct = structNew()>
    <cfset returnStruct.datetime = "">
    <cfset returnStruct.isConverted= false>
<cftry>
    <cfset date = trim(left(trim(date), 11)) />
    <cfset time = trim(left(trim(time), 5)) />
    <cfset dateArr = listToArray(date, " ") />
    <cfset dateArr[2] = replace(dateArr[2], "Jan", 1) />
    <cfset dateArr[2] = replace(dateArr[2], "Feb", 2) />
    ...etc...
    <cfset dateArr[2] = replace(dateArr[2], "Dec", 12) />
    <cfset dateTime = ArrayToList(dateArr, " ")&" "&time />
    <cfset dateTimeBits = listToArray(dateTime, " :") />
    <cfset ODBCdateTime = CreateODBCDateTime(CreateDateTime(dateTimeBits[3], dateTimeBits[2], dateTimeBits[1], dateTimeBits[4], dateTimeBits[5], 0)) />
    <cfset returnStruct.unixDateTime = DateDiff("s", CreateDate(1970,1,1), ODBCdateTime) />
    <cfset returnStruct.message = "Conversion succeeded.">
    <cfset returnStruct.isConverted= true>
    <cfreturn  returnStruct>
<cfcatch>
    <cfset returnStruct.message = cfcatch.message>
    <cfreturn  returnStruct>
</cfcatch>
</cftry>
</cffunction>

<cffunction name="convertUTStoDate" output="no" returntype="struct">
     <cfargument name="uts" required="Yes" />
     <cfset var returnStruct = structNew()>
     <cfset returnStruct.datetime = "">
     <cfset returnStruct.isConverted= false>
<cftry>
     <cfset date = DateFormat(DateAdd("s",uts,"1970/01/01 00:00:00"),"DD MMM YYYY") />
     <cfset time = TimeFormat(DateAdd("s",uts,"1970/01/01 00:00:00"), "HH:mm") />
     <cfset returnStruct.datetime = date&" "&time />
     <cfset returnStruct.message = "Conversion succeeded.">
     <cfset returnStruct.isConverted= true>
     <cfreturn  returnStruct>
<cfcatch>
      <cfset returnStruct.message = cfcatch.message>
      <cfreturn  returnStruct>
</cfcatch>

</cftry>
</cffunction>

This does the conversion correctly but it it won't let me use it as the condition in a CFIF like the first function does eg <cfif convertUTStoDate(uts)> but, it does work exactly as I want if I do this: <cfif convertUTStoDate(uts) NEQ FALSE> What am I doing wrong?

The expression <cfif convertUTStoDate(uts)> will only work if ColdFusion can cast convertUTStoDate(uts) to a boolean. That is in turn possible only if that value is a boolean or a number. It fails bacause convertUTStoDate(uts) is a date.

However, the expression <cfif convertUTStoDate(uts) NEQ FALSE> is a comparison. As such, it will always work, so long as convertUTStoDate(uts) is a simple value. It will then be comparing like with like.

I'm surprised the first function worked.  Using strings as booleans just seems wrong.  I would suggest using an empty string as your return value if the conversion fails and using your if/else logic on the length of the returned value.