oh, yes, in rust coroutines do not normally allocate as far as I understand. This is not the case in C++ unfortunately. This was extremely contentious to say the least, but all alternative designs were either very unsafe or were presented very late, so the committee has preferred to go with something working now instead of something perfect in an indeterminate future.
There are already proposals to improve on the design, but we will have to see if they work out.
