Re: [xsl] Cheaper to prepend or append an item to a sequence?

[Michael Kay <mike@xxxxxxxxxxxx>]

> > Even with a forward-chained list, you can implement append without copying
> > if you choose, at least for the first append operation to a given list
> > (which 9 times out of 10 will be the only append operation).
> How is that?  If I have X=[1,2,3] ; Y=X ; Z=Y++[4]
>
> How can Z append Y without copying it first?

When one list A is a sublist of another list B, A does not need separate 
storage - it can be implemented by means of pointers to the first and 
last items from B that are to be included in A. Therefore if A is not 
already a sublist of another list, you can create B by making a longer 
list and making A a sublist of the new list. Saxon does this using 
arrays rather than linked lists, but the same principle would work 
either way.

Michael Kay
Saxonica