It cannot be more "performant". The design of demand-driven futures is used because it allows "zero-cost futures". Specifically poll()ing the Future is required

It cannot be more "performant". The design of demand-driven futures is used because it allows "zero-cost futures". Specifically poll()ing the Future is required to drive it, and drop()ping the Future frees its resources. Both of these require another future or the executor itself to be the parent of every future, rather than the future driving itself. But also the performance is not likely something to worry about. I've never measured it myself but I do know aturon posted that he could not find any measurable effect of having deep future stacks. It is noticeable in the sense that a big enough stack may exceed your OS's limit (especially on Windows where the main thread defaults to a 1MiB stack).