The subject of the function coloring article was callback APIs in Node, so an argument you need to pass to your IO functions is very much in the spirit of colored functions and has the same limitations.
The coloring is not the concrete argument (Io implementation) that is passed, but whether the function has an Io parameter in the first place. Whether the implementation of a function performs IO is in principle an implementation detail that can change in the future. A function that doesn't take an Io argument but wants to call another function that requires an Io argument can't. So you end up adding Io parameters just in case, and in turn require all callers to do the same. This is very much like function coloring.
In a language with objects or closures (which Zig doesn't have first-class support for), one flexibility benefit of the Io object approach is that you can move it to object/closure creation and keep the function/method signature free from it. Still, you have to pass it somewhere.
> Whether the implementation of a function performs IO is in principle an implementation detail that can change in the future.
I think that's where your perspective differs from Zig developers.
Performing IO, in my opinion, is categorically not an implementation detail. In the same way that heap allocation is not an implementation detail in idiomatic Zig.
I don't want to find out my math library is caching results on disk, or allocating megabytes to memoize. I want to know what functions I can use in a freestanding environment, or somewhere resource constrained.
> Performing IO, in my opinion, is categorically not an implementation detail. In the same way that heap allocation is not an implementation detail in idiomatic Zig.
It seems you two are coming at this from opposing perspectives. From the perspective of a library author, Zig makes IO an implementation detail, which is great for portability. It lets library authors freely use IO abstractions if it makes sense for their problem.
This lets you, as an application developer, decide the concrete details of how such libraries behave. Don't want your math library to cache to disk? Give it an allocating writer[0] instead of a file writer. Want to use an library with async functionality on an embedded system without multi threading? Pass it a single threaded io[1] runtime instance, implement the io interface yourself as is best for your target.
Of course someone has to decide implementation details. The choices made in designing Zig tend to focus on giving library authors useful abstractions thst give application authors meaningful control over important decisions for their application.
The problem with function coloring is that it makes libraries difficult to implement in a way that's compatible with both sync and async code.
In Python, I needed to write both sync and async API clients for some HTTP thing where the logical operations were composed of several sequential HTTP requests, and doing so meant that I needed to implement the core business logic as a Generator that yields requests and accepts responses before ultimately returning the final result, and then wrote sync and async drivers that each ran the generator in a loop, pulling requests off, transacting them with their HTTP implementation, and feeding the responses back to the generator.
This sans-IO approach, where the library separates business logic from IO and then either provides or asks the caller to implement their own simple event loop for performing IO in their chosen method and feeding it to the business logic state machine, has started to appear as a solution to function coloring in Rust, but it's somewhat of an obtuse way to support multiple IO concurrency strategies.
On the other hand, I do find it an extremely useful pattern for testability, because it results in very fuzz-friendly business logic implementation, isolated side-effect code, and a very simple core IO loop without much room in it for bugs, so despite being somewhat of a pain to write I still find it desirable at times even when I only need to support one of the two function colors.
My opinion is that if your library or function is doing IO, it should be async - there is no reason to support "sync I/O".
Also, this "sans IO" trend is interesting, but the code boils down to a less ergonomic, more verbose, and less efficient version of async (in Rust). It's async/await with more steps, and I would argue those steps are not great.
From a performance perspective, asynchronous IO makes a lot of sense when you're dealing concurrently with a large number of tasks which each spend most of their time waiting for IO operations to complete. In this case, running those tasks in a single-threaded event loop is far more efficient than launching off thousands of individual threads.
However, if your application falls into literally any other category, then suddenly you are actually paying a performance penalty, since you need the overhead of running an event loop any time you just want to perform some IO.
Also, from a correctness perspective, non-concurrent code is simply a lot less complex and a lot harder to get wrong than concurrent code. So applications which don't need async also end up paying a maintainability, and in some cases memory safety / thread safety, penalty as well.
The beautiful thing about the “async” abstraction is that it doesn’t actually tie you to an event loop at all. Nothing about it implies that somebody is calling `epoll_wait` or similar anywhere in the stack.
It’s just a compiler feature that turns functions into state machines. It’s totally valid to have an async runtime that moves a task to a thread and blocks whenever it does I/O.
I do agree that async without memory safety and thread safety is a nightmare (just like all state machines are under those circumstances). Thankfully, we have languages now that all but completely solve those issues.
You surely must be referring to Rust, the only multithreaded language with async-await in which data races aren't possible.
Rust is lovely and all, but is a bad example for the performance side of the argument, since in practice libraries usually have to decide on an async runtime, so in practice library users have to launch that runtime (usually Tokio) to execute the library's Futures.
Sure, but that’s a library limitation (no widespread common runtime interface that libraries such as Tokio implement), not a fundamental limitation of async.
Thread safety is also a lot easier to achieve in languages like C#, and then of course you have single-threaded environments like JS and Python.
Exactly, there is nothing wrong with function coloring. It's a design choice.
Colored functions are easier to reason about, because potential asynchronicity is loudly marked.
Colorless functions are more flexible because changing a function to be async doesn't virally break its interface and the interface of all its callers.
Zig has colored functions, and that's just fine. The problem is the (unintentional) gaslighting where we are told that Zig is colorless when the functions clearly have colors.
As mentioned, the problem with coloring is not that you see the color, the problem is that you can't abstract over the colors.
Effectful languages basically add user-definable "colors", but they let you write e.g. a `map` function that itself turns color based on its parameter (e.g. becoming async if an async function is passed).
I think talking about colouring often misses the point. Sync & async code are fundamentally different; languages without coloured functions make everything async. Everything in go (for instance) is running in an async runtime, and it's all preemptable.
> I don't want to find out my math library is caching results on disk, or allocating megabytes to memoize. I want to know what functions I can use in a freestanding environment, or somewhere resource constrained.
On that vein, I would often like to know whether the function I can is creating a task/thread/greenlet/whatever that will continue executing, concurrently, after it returns. Making that be part of the signature is approximately called “structured concurrency”, and Zig’s design seems to conflate that with taking an io parameter. This seems a bit disappointing to me.
> A function that doesn't take an Io argument but wants to call another function that requires an Io argument can't.
Why? Can’t you just create an instance of an Io of whatever flavor you prefer and use that? Or keep one around for use repeatedly?
The whole “hide a global event loop behind language syntax” is an example of a leaky abstraction which is also restrictive. The approach here is explicit and doesn’t bind functions to hidden global state.
Is that a problem in practice though? Zig already has this same situation with its memory allocators; you can't allocate memory unless you take a parameter. Now you'll just have to take a memory allocator AND an additional io object. Doesn't sound very ergonomic to me, but if all Zig code conforms to this scheme, in practice there will only-one-way-to-do-it. So one of the colors will never be needed, or used.
