Re: Recommended way to get an empty XdmSequenceIterator?

Thanks for raising it. I think the simplest solution is to change XdmValue.iterator() to declare its return type as XdmSequenceIterator.

Michael Kay
Saxonica

> On 17 Oct 2020, at 00:46, Chapman Flack <chap-JULfBfA8satPFr4CO1/[email protected]> wrote:
> 
> Hi,
> 
> I have a simple case where ordinarily I will get an
> XdmSequenceIterator<XdmItem> as the result of XQueryEvaluator.iterator(),
> and pass that to a consumer method that does expect an
> XdmSequenceIterator<XdmItem> (so as to be able to close it, if
> the full result isn't needed).
> 
> But in another case that's detectable, I should skip the evaluator and
> just pass the consumer method an empty XdmSequenceIterator<XdmItem> instead.
> 
> My first instinct was to use XdmEmptySequence.getInstance().iterator(),
> but that returns a java.util.Iterator, not an XdmSequenceIterator.
> 
> I seem to have been getting away with casting that java.util.Iterator
> to an XdmSequenceIterator<XdmItem>, but it seems a bit smelly to assume
> that is what will be returned, and cast to an assumed generic type.
> 
> I could import EmptyIterator from net.sf.saxon.tree.iter and construct
> an XdmSequenceIterator from an instance of that. But then I end up
> suppressing both an unchecked-cast and a raw-type warning, because the
> XdmSequenceIterator constructor returns a raw type.
> 
> So I think for now I will stick with the assumption and cast.
> 
> Maybe XdmSequenceIterator should just have an emptyIterator() method of
> its own?
> 
> Or perhaps a generic
> 
> static <T extends XdmItem>
>  XdmSequenceIterator<T> of(java.util.Iterator<T> iter)
> 
> that just returns an appropriately-typed XdmSequenceIterator whose close()
> does nothing, from an arbitrary java.util.Iterator?  It could internally
> just be a cast, if the argument is already an XdmSequenceIterator.
> 
> Regards,
> -Chap
> 
> 
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