The new Zig IO will essentially be colored, but in a nicer way than Rust.
You don't have to color your function based on whether you're supposed to use in in an async or sync manner. But it will essentially be colored based on whether it does I/O or not (the function takes IO interface as argument). Which is actually important information to "color" a function with.
Whether you're doing async or sync I/O will be colored at the place where you call an IO function. Which IMO is the correct way to do it. If you call with "async" it's nonblocking, if you call without it, it's blocking. Very explicit, but not in a way that forces you to write a blocking and async version of all IO functions.
The Zio readme says it will be an implementation of Zig IO interface when it's released.
I guess you can then choose if you want explicit async (use Zig stdlib IO functions) or implicit async (Zio), and I suppose you can mix them.
> Stackful coroutines make sense when you have the RAM for it.
So I've been thinking a bit about this. Why should stackful coroutines require more RAM? Partly because when you set up the coroutine you don't know how big the stack needs to be, right? So you need to use a safe upper bound. While stackless will only set up the memory you need to yield the coroutine. But Zig has a goal of having a built-in to calculate the required stack size for calling a function. Something it should be able to do (when you don't have recursion and don't call external C code), since Zig compiles everything in one compilation unit.
Zig devs are working on stackless coroutines as well. But I wonder if some of the benefits goes away if you can allocate exactly the amount of stack a stackful coroutine needs to run and nothing more.
This is not true. Imagine code like this:
Can you guess if it's going to do blocking or non-blocking I/O read?The io parameter is not really "coloring", as defined by the async/await debate, because you can have code that is completely unaware of any async I/O, pass it std.Io.Reader and it will just work, blocking or non-blocking, it makes no difference. Heck, you even even wrap this into C callbacks and use something like hiredis with async I/O.
Stackful coroutines need more memory, because you need to pre-allocate large enough stack for the entire lifetime. With stackless coroutines, you only need the current state, but with the disadvantage that you need frequent allocations.
> Stackful coroutines need more memory, because you need to pre-allocate large enough stack for the entire lifetime. With stackless coroutines, you only need the current state, but with the disadvantage that you need frequent allocations.
This is not quite correct -- a stackful coroutine can start with a small stack and grow it dynamically, whereas stackless coroutines allocate the entire state machine up front.
The reason why stackful coroutines typically use more memory is that the task's stack must be large enough to hold both persistent state (like local variables that are needed across await points) and ephemeral state (like local variables that don't live across await points, and stack frames of leaf functions that never suspend). With a stackless implementation, the per-task storage only holds persistent state, and the OS thread's stack is available as scratch space for the current task's ephemeral state.
> You don't have to color your function based on whether you're supposed to use in in an async or sync manner. But it will essentially be colored based on whether it does I/O or not (the function takes IO interface as argument). Which is actually important information to "color" a function with.'
The Rust folks are working on a general effect system, including potentially an 'IO' effect. Being able to abstract out the difference between 'sync' and 'async' code is a key motivation of this.