A tweak was made to the design of coroutines in 2018 to add a capability called “symmetric transfer” which allows you to suspend one coroutine and resume another coroutine without consuming any additional stack-space. The addition of this capability lifted a key limitation of the Coroutines TS and allows for much simpler and more efficient implementation of async coroutine types without sacrificing any of the safety aspects needed to guard against stack-overflow. In this post will attempt to explain the stack-overflow problem and how the addition of this key “symmetric transfer” capability lets us solve this problem.