You can't just allocate a Lua coroutine on the heap. Lua coroutines are managed by the Lua virtual machine. So that's one heap allocation "avoided". I don't remember the others off the top of my head but some functions needed to have three lifetimes for various reasons. Not sure if I eventually refactored that out or not, it's been a while. I should get back to it one day when my job isn't nothing but startup crunching