Why is ListAppend non destructive, while ArrayAppend and StructInsert are both destructive?

Question

I just spent almost an hour trying to figure out an issue with having a list that would always return an empty string. I was using ListAppend just like one uses ArrayAppend or StructInsert, but apparently ListAppend works differently. What, if any, is the reasoning behind having ListAppend work differently from everything else?

<cfset ListAppend(list, item)>

list = ''

<cfset ArrayAppend(array, item)>

array[1] = item

<cfset StructInsert(struct, 'key', item)>

struct.key = item

Answer 1

Possibly because a list is just a big String. Unlike arrays and structures, Strings are immutable, meaning they cannot be changed. To "append" a new value, you need to create an entirely new String. Arrays and structures are mutable. So you can modify them "in place".

Answer 2

Lists in ColdFusion are just Strings and strings in ColdFusion (and Java) are immutable. They cannot be changed. So ListAppend() must return the a new string with the value instead of modifying the existing string.

<cfset newList = listAppend(oldList, "New Value") />