Is that a given, though? Rust's generators are decent prior art - they generate a state machine that would only require heap allocation if the size of the state machine becomes unbounded (for example, a recursive generator). Otherwise the generator is perfectly capable of being stack allocated in its entirety. This turns out to be sufficient for a large amount of programs, with a sufficient workaround for the ones where you can't (box the generator, making the allocation explicit).
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.
