As integers are "movable" (moving them in C++ just copies them, but you can call std::move), implementations of algorithms like std::sort tend to assume they ar

As integers are "movable" (moving them in C++ just copies them, but you can call std::move), implementations of algorithms like std::sort tend to assume they are only allowed to move things. You could in principle write two implementations, one that moves + swaps, and one that moves, swaps and (occasionally if it really wants to) copies, but it's extremely hard (possibly impossible) to decide when it is "safe" to use the std::sort that can copy. It turns out it is much easier to optimise if you can copy the pivot into a local variable, but that's hard to do in std::sort.