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  • $\begingroup$ Leonid, what a solution, thank you. I had believed there is some 'easy' way - possibly upvalues - but your answer shows how deep the matter runs. $\endgroup$ Commented Jun 22, 2012 at 13:47
  • $\begingroup$ @gwr Thanks :). In fact, since Part is overloaded via UpValues, and then only for Set, and part assignments for indexed symbols are normally prohibited anyway, I would even think that globally overloading Part could be ok (i.e. doing the same thing but without the dynamic invironment), in which case, you don't have to wrap your code in it. But, it is still better to be on the safe side, all it takes is just to wrap your top-level function(s) in withModifiedPart. Thanks for the accept as well. $\endgroup$ Commented Jun 22, 2012 at 13:50
  • $\begingroup$ +1, nice one! What's the purpose of setting the DownValue by hand only when there's no other downvalue associated with the symbol, versus simply sym[index]=ref? $\endgroup$ Commented Jun 22, 2012 at 13:52
  • $\begingroup$ @Rojo Thanks:). As to the reason for my construct: because I already overload Set on this symbol, I can not use it (Set) to set the DownValue, since the new definition will be used, and we will enter an infinite recursion. $\endgroup$ Commented Jun 22, 2012 at 13:54
  • $\begingroup$ Right, and furthermore you avoid creating a different symbol every time a certain index is reassigned a new value, leaking memory. My yet-non-DownValues-user instinct would have led me to tackle both issues differently. Using explicit DownValues is something that doesn't come straight to mind $\endgroup$ Commented Jun 22, 2012 at 14:07