On Thu, Jun 13, 2013 at 12:16 PM, Kevin Gadd <[email protected]> wrote:
> I don't understand why you would intentionally sidetrack a discussion > about a simple problem with academic details. > He brings up a very real point, which is that you can't realistically have an "always unstable" sort. If I understand you correctly, what you want by an "always unstable" sort is that you want developers to "get bitten" in testing due to instability, even for small test cases, so that the issue is caught earlier. The problem with that desire is that there are no sorting algorithms AFAIK that guarantee that they will *always* rearrange equal-sorting elements (i.e., "always unstable"): even a pure recursive quicksort (no insertion-sort base case) will sometimes not rearrange equal-sorting elements (i.e., seem stable). If I understand your desire correctly, then what you're asking for by "always unstable" is to require that if an implementation's sorting algorithm *might* rearrange equal-sorting elements, then it must *always* go out of its way to ensure that if equal-sorting elements are present, then it does not preserve their order; I haven't looked in detail at what this would mean from an implementation standpoint, but I'm pretty sure that it is unrealistic. -- Sean Silva
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