async fn write_buffer(buf: &mut [u8]) -> Ticket<BufferWritten>

//Best that it it's own function for readability

async fn complex_counter_logic(ctr: Arc<AtomicUsize>, ticket: Ticket<BufferWritten>) -> Ticket<ComplexCounterLogic>

//One could also place all the data in a giant struct and move that across all functions but that eventually leads to struct bloat unless we use an explicit state machine, in which case type state is better

func1(foo_0) -> bar0

func2(foo_1, foo_2) -> bar1

func3(foo_3, foo_3) -> bar2

And you wanted to make sure that func2 and func3 can only be called after func1 has been called.

A wrapper on the output of func1 here would be awkward because then you return Wrapper<Func1Done>(bar0). But func2 does not even need a bar0 and neither does func3.

So the solution is to return (bar0, Wrapper<Func1Done>) from func1 where

struct Wrapper<T>(//cheating ())