ColdFusion Quiz, Part 2

I now know how Howard Dean must feel after his "I Have a Scream" speech in Iowa. Ray Camden was kind (and smart!) enough to point out that I misspoke in one of the answers I gave. The problem in question was number 6. Here it is again:

6. Given this CFC:

<cfcomponent displayname="Classroom">
   <cfset variables.students = ArrayNew() />
   <cfset variables.teacher = "" />
	
   <cffunction name="addStudent" returntype="void">
      <cfargument name="student" type="Student" required="true">
      <cfset ArrayAppend(getStudents(), arguments.student) />
   </cffunction>
	
   <cffunction name="getStudents" returntype="array">
      <cfreturn variables.students />
   </cffunction>
</cfcomponent>

You create 1 "Classroom" object, "classroom", and 3 Student objects. You call the "addStudent()" method, passing in each of the three new students. At the end of this, what will this code produce?

#ArrayLen(classroom.getStudents())#

There were actually two errors. The first was a typo: there is no dimension given in the "ArrayNew()" function call. It should be "ArrayNew(1)". Simple enough -- but the second one is trickier. I said that the code would produce zero. But that's incorrect, Ray pointed out. It will produce three, not zero. When I read Ray's email, shudders of horror overcame me: the CFDJ article describing my solution was already being printed. Could I really have goofed up that badly? Granted, I did write the article at 3.00 am having just gotten back from a training trip, but still...

The issue I refer to is real, but the code I provided doesn't illustrate the problem. To see the problem, the method, "addStudent", should look like this:

   <cffunction name="addStudent" returntype="void">
      <cfargument name="student" type="Student" required="true">
      <cfset var students = getStudents() />
      <cfset ArrayAppend(students, arguments.student) />
   </cffunction>

Now, because of the way arrays are passed in CF (by value and not by reference), the variable, "students", is actually a copy of "variables.students". But this only comes into play if I add the "var students" line. Is the issue solved simply by keeping the code as I originally wrote it intact?

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Unfortunately, you can't always do this. Let's say that we want to add a method to "Classroom" called "removeStudent". The method accepts a "Student" object and, if the student is found in "students", will remove the student from the array. The code for it might look something like this:

   <cffunction name="removeStudent" returntype="boolean">
      <cfargument name="student" type="Student">
      <cfloop from="1" to="#ArrayLen(getStudents())#" index="i">
         <cfif getStudents()[i].getName() EQ arguments.student.getName()>
            <cfset ArrayDeleteAt(students, i) />
         </cfif>
      </cfloop>
   </cffunction>

I say it might look like that, but in fact, that code won't compile. You just can't use "getStudents()[i]". Instead, you need something like this:

   <cffunction name="removeStudent" returntype="boolean">
      <cfargument name="student" type="Student">
      <cfset var students = getStudents()>
      <cfloop from="1" to="#ArrayLen(students)#" index="i">
         <cfif students[i].getName() EQ arguments.student.getName()>
            <cfset ArrayDeleteAt(students, i) />
         </cfif>
      </cfloop>
   </cffunction>	

Now, for this particular example, you could do this:

   <cffunction name="removeStudent" returntype="boolean">
      <cfargument name="student" type="Student">
      <cfset var students = getStudents()>
      <cfloop from="1" to="#ArrayLen(students)#" index="i">
         <cfif students[i].getName() EQ arguments.student.getName()>
            <cfset ArrayDeleteAt(getStudents(), i) />
         </cfif>
      </cfloop>
   </cffunction>	

That will work for this particular method, but there will be other methods where manipulating a copy of "students" (which is what I've done in the above code) just won't work: you need access to the actual underlying instance variable, "students". If you're interested in a more universal solution, check out my column in the next CFDJ.

Many thanks to Ray for alerting me to my error. Now, I have to go on Dianne Sawyer, as Mr. Dean did, and cover myself in mea culpas.