ColdFusion 8's CFLoop Passes Array By Reference?

I was just having a little comment-conversation with Scott Bennett over on another post about the difference between CFScript and tag-based looping when I had a thought - if CFLoop tag attributes are only evaluated ONCE when the tag is initially fired (with the exception of the Condition attribute which does not use hash signs), does that mean that the Array attribute new to ColdFusion 8 passed arrays by reference or by value?

To test this, I set up a simple CFLoop scenario in which the array was truncated during loop execution:

As you can see, we are passing the array, arrGirls, to the CFLoop tag using hash signs. Experience would lead us to believe that this means pass by value and is evaluated only once. During the loop, I then check for array items and delete from the end. Running this code, we get the following output:

Sarah
Michelle
CFERROR Has Fired With The Following Error - Array index out of range: 2 null

As you can see, when we get half way through the iteration, we have deleted enough tail items from the original array to cause the loop to run out of bounds. This would only happen if the array was passed to the CFLoop context by reference. Had it been passed by value, the ArrayDeleteAt() would NOT have affected the array stored internally to the CFLoop tag context.

What about the other way? That's how the CFLoop responds to modification by deletion, but how does it respond to modification by appending? In this next example, as we iterate over the array, we are going to be adding items to it:

When we run this code, we get the following output:

data1
data2

That's what is output during the CFLoop execution, but here's what the final CFDump reveals:

Interesting! Here's we have a little bit of a conflict! The CFLoop executed as if the array was being passed by value and was not acknowledging the modifications to the array that were made during the loop body. So now, we have one example that makes us think pass by reference and one execution that makes us think pass by value.

When you think about what both examples have in common, it starts to become clear what's going on - ColdFusion 8's new Array-CFLoop functionality is merely performing an index loop behind the scenes. When we write:

... we can visualize this as working inside a ColdFusion Custom tag like this (pseudo code style):

In this case, it doesn't matter if the array is being passed by value OR by reference - the underlying algorithm is only using the array length ONCE during initial tag execution. Then, going forward, throughout the body of the CFLoop tag, it is referring to the original array pointer; the passed reference is never used again.

This is what I theorize, but I think it makes sense.

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