Nordlöw:
Couldn't we do a first pass and check that if elements of T are distinct and if so set doCopy to false otherwise true?
The algorithm you have seen in Rosettacode doesn't care if and what items of the input sequence are duplicated, it handles them as they are all distinct. And them being distinct (or not distinct) doesn't change the desire to use something like doCopy to have dup-ped output arrays, so I don't understand what you are trying to say.
The purpose of doCopy is similar of the difference between File.byLine and File.byLineCopy (originally I suggested to give a doCopy argiment to byLine too, for safety. Andrei said no. Later experience has shown I was right and we have added byLineCopy, but now the default line iteration is the non-copying one, that is less safe).
Bye, bearophile
