Saxon

Noted. It seems the "good" message is coming when we do array:get() on a SimpleArrayItem, and the "bad" message is coming when we do array:get() (or put()) on an ImmutableArrayItem. These are just two different internal implementations of XDM arrays; the SimpleArrayItem is used for arrays that have not undergone any incremental modifications, while the ImmutableArrayItem is used when there have been such modifications or where we think they are likely.

For 10.0 I have changed the approach for bounds-checking, which is currently very haphazard.

(a) the code for the specific array function (e.g array:get(), array:put()) checks the subscript before calling underlying methods on the XdmArray object

(b) the XDM array object's methods (get, put, remove) -- which use zero-based subscripts -- are declared to throw IndexOutOfBoundsException if the subscript is out of range; but this won't happen for a direct call from a function such as array:get(), because the value will already have been checked

(c) the responsibility for checking (b) rests with the implementation class, e.g. SimpleArrayItem or ImmutableArrayItem.

(d) we don't attempt to catch the IndexOutOfBoundsException because it should never happen.

For 9.9 I will make a more modest change that only affects ImmutableArrayItem.get().

A further patch has been committed fixing the error handling on array lookup expressions such as $A?23.