Yep, I'm not arguing that it's always a good idea (or even usually...or even that I've seen it be a good idea in the wild), just that it could be. Taking quicks

Yep, I'm not arguing that it's always a good idea (or even usually...or even that I've seen it be a good idea in the wild), just that it could be. Taking quicksort as an example, it's only constant space if you're allowed/able to mutate in-place. If you need (for some bizarre reason) to stream sorted results in constant space without mutating the underlying data then you'll need some other tool.