Bug in Linked Lists?

[Kevin Crowston]

I think I have found a bug in the List type collections.  I have a list of
numbers, and am trying to delete duplicates.  Here's a code fragment:


  [point setLoc: Start] ;
  next = (int)[point next] ;
  while ( [point getLoc] == Member ) {
    if ( nextVect[next] == 0 )
      nextVect[next] = -1 ;
    else
      [point remove] ;
    next = (int)[point next] ;
  }

(point is a previously created ListIndex, i.e., point = [list begin:...] )

The nextVect[next] is used to keep track of which elements I've already
seen and is initially all 0's (I created the array for use in the next
step, so I figured I'd just reuse it here).

I'm using the [point getLoc] == Member construction because the list
contains integers, including 0 (meaning that nil is a perfectly acceptable
return value).

Okay--without looking, can you figure out what the fragment leaves in the list?


The bug is that the list ends up empty.  Apparently when I remove the last
item in the list, the next next puts me back to the beginning--so I go
through the list a second time and this time delete everything, thinking
it's a repeat.

The documentation says that removing the last element leaves you at End,
but in fact it leaves you with [point getLoc] == "Removed".  Doing a next
from this Removed node seems to take you to the front of the list.

Kevin



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