Async/await in Rust is famously not based on continuations, at least not in any traditional sense, where a block of code is passed to a reactor system to be inv

Async/await in Rust is famously not based on continuations, at least not in any traditional sense, where a block of code is passed to a reactor system to be invoked whenever an operation completes. Instead it is based on "wakers", which are objects associated with a task, and can be used to notify the task's executor that the task is ready to make progress. It is then the job of an executor resume the task. So there is an extra layer of indirection (conceptually). There are pros and cons, but in essence the system trades a check on resume (often redundant) for the need to make a heap allocation and/or type erasure at each await point. (It's possible to avoid the latter in continuation-based implementations, like C++ coroutines, but it's pretty hard.)