Andrew's ramblings

Follow up to flaw using local variable in ColdFusion 9

Tags: Coldfusion

It seems that a minority of people do not seem to understand the actual problem in my previous post, so I thought I would make a few changes to give a better description of the problem.

But first lets look at ColdFusion 8 for a moment.

ColdFusion prior to ColdFusion 9, had no concept of private variables in functions and this was a major issue, when it came to thread safe components and methods.

ColdFusion introduced the var keyword to help, but this was a real after thought and was full of problems right from the beginning but it was the best we had at the time.

So in a method in a component it is very legal to write code like this.

Now lets get this straight, I am not one to use it this way. However I can see benefits to doing this and I'll describe that in a minute. In ColdFusion 8 this will return a struct and define it to the variable scope local, in ColdFusion 9 the function call is totally ignored.

So even though this line of code is exactly the same as doing this.

Which both ColdFusion 8 and ColdFusion 9 will happily run.

The major problem now is trying to follow DRY (Don't repeat yourself) pattern, so if you find yourself defining a structure in the same manner it makes extreme sense to refactor your code to call a method to return the structure. Which is how this problem has risen.

So for some reason even though ColdFusion will except an explicit struct definition, it will not accept a function returning any structure, it will just not run that function.

So lets look at the next problem this creates, and that would be to refactor the code to look something like this.

And why is this a problem, well it is a problem because it now does a very weird thing in ColdFusion 9, which doesn't happen in ColdFusion 8.

That is that the first line sets up a local structure, but the second one defines the local back into a variables scope. This can be seen in the line debugger as such or you can do this to test it for yourself.

And to make it even worse for ColdFusion 9. If I then create some code to do this.

These are stored in the first local definition, so we ColdFusion has now ended up with 2 local variables, one the local scope the second as a struct in the variables scope.

I hope this clears it up some more, this will break existing ColdFusion 8 applications and Adobe has tried to be backward compatible, but anyone who uses this method is going to have to refactor their code.