[infinispan-dev] QueryIterator inconsistencies

[Marko Lukša]

Hey

Infinispan's implementations of QueryIterator don't conform to the 
contract of ListIterator and are pretty buggy (see 
https://issues.jboss.org/browse/ISPN-2337). The most important bug is 
the fact that calling next() and then previous() should return the same 
element, but it doesn't.

I'm trying to fix the bugs, but have now realized that even the 
interface QueryIterator is problematic.

1.  QueryIterator.first()
This one isn't as problematic as the next ones, but it's strange that 
calling first() and then next() returns the first element of the 
collection. It would be clearer if the method were called 
"beforeFirst()" or something similar.

2. QueryIterator.last()
What should the iterator return when you call last() and then call 
next()? What about if you call last() and then previous()? A user would 
probably call last() as the first step of iterating over the results 
backwards. So calling previous() should return the last element. The 
method should probably be renamed to "afterLast()".

3. QueryIterator.afterFirst() & beforeLast()
These two are OK. Calling next() after afterFirst() should return the 
second element, while calling previous() should return the first element.

4. isFirst(), isLast()
ListIterator does not have the concept of "current element", but the 
javadoc of all the is*() methods talk about the current element, which 
is ambiguous. Therefore isFirst() and isLast() should probably be 
renamed to isBeforeFirst() and isAfterLast().

5. jumpToResult(int index)
When jumping to index=1, what does next() return? What about previous()? 
We should probably replace the method with two others: beforeResult(int 
index) and afterResult(int index)

Any comments / other ideas?

Marko