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Comment by throw10920 | Hacker News Reader

> Knowing ahead of time which functions are async is a feature.

"Expensive" is subjective and should be up to the programmer to decide.

And, it absolutely should not require creating two identical function definitions to get around the function coloring problem - that's completely indefensible.

> This is a good thing for programmers to easily see and know at the call site.

Yes, and the IDE can show you that information, exactly like it does the types of arguments. We don't redundantly write the types of arguments at the call site because it's a good thing for programmers to see (which it is), we let the IDE do that.

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> And, it absolutely should not require creating two identical function definitions to get around the function coloring problem - that's completely indefensible.

Oh yes, absolutely. But the solution to that is stop using joke languages that can't do kind polymorphism.

> Yes, and the IDE can show you that information, exactly like it does the types of arguments.

How can it, if the language doesn't give it that information? Either you have a language that can reliably distinguish between sync and async calls in a standard way - which is to say, it has a type system that distinguishes between sync and async, whether it calls it that or not - or your IDE has an ad-hoc informally specified bug-ridden slow implementation of half of one.

Good luck with that, when we keep using glue languages for full blown applications, and then shelling out to C extensions, instead of ones that could do the job all by themselves.

> And, it absolutely should not require creating two identical function definitions to get around the function coloring problem - that's completely indefensible.

This is very rarely necessary in app code. It's usually only a pattern for higher-level utility functions, and even then if you really wanted to you could unify implementations with generators.

> And, it absolutely should not require creating two identical function definitions to get around the function coloring problem - that's completely indefensible.

I'm afraid I don't follow. It's impossible for you to have two identical functions (one sync and one async), since then they would both be sync. What did you mean?

Two functions that are identical up to one of them being async and using "await" to call another function foo_async, and the other that is sync and calling foo_sync (a synchronous version of foo_async) without await?

I think the only place that happens is in programming languages where you actually can choose to do something using a thread-blocking operation? Specifically, I've only seen it in Python. And yeah, it's not very ideal there. In other languages, it's typically only possible to do the operation in async mode, so you never write a foo_sync function in the first place.

The "it's typically only possible to do the operation in async mode" is part of the problem. If I'm writing a a batch script that parses a file as part of its operation, I don't want or need the read_file() function to be async! My code should just block until the file opens.

Alternately, I want to be able to designate a computationally-intense function call (just that call, leaving the other calls alone) as async so that control yields to the event loop.

The main problem is that someone got it in their head that the function definition was the right place to designate whether a function was async or not, and it's not. The right place is the call site.

> The main problem is that someone got it in their head

This unnecessarily trivializes the technical problems at hand. This wasn't just something someone got in their head, especially considering...

> that the function definition was the right place to designate whether a function was async or not, and it's not. The right place is the call site.

This is exactly what JavaScript did. The program only yields at `await`ed callsites and doesn't yield at all other callsites.

`async` only tells the VM to create the state machine necessary to resume the function after `awaited` calls return.

> This unnecessarily trivializes the technical problems at hand.

Making a language that automatically generates two versions of a function, one that is async and returns a Promise-wrapped object, and another that is sync, is not hard.

> This is exactly what JavaScript did.

No, it isn't. JavaScript requires you to declare functions as async at the function definition, and you can't call async functions from sync ones. This is exactly the thing I am arguing against, and is the opposite of "The right place is the call site."

If it wasn't hard, it would have been done. I suppose we should all await your backwards compatible proposal?

> No, it isn't.

Yes, actually, it is. Async functions are a concept that only affects the internal structure of a function - to generate the state machine that allows yielding at `await` keywords and resuming after they resolve. Externally they are no different from "sync" Promise-returning functions.

So they only thing that async functions do is enable yielding at the callsite, the `await` keyword is what actually yields at the callsite and you can await anything, not just async functions.

Again:

> I want to be able to designate a computationally-intense function call (just that call, leaving the other calls alone) as async so that control yields to the event loop.

This is what `await` is - `await` yields. Non-await calls don't yield.

> If it wasn't hard, it would have been done.

This comment shows a true departure from reality. Computing is filled to the brim with ideas that are easy but are not implemented for reasons other than difficulty.

> I suppose we should all await your backwards compatible proposal?

Your sarcasm merely helps to further demonstrate that you're not interested in a serious discussion.

> Yes, actually, it is.

Then it should be trivial for you to show me an instance of a sync function calling an async one, synchronously waiting for it, then getting back the return value, without clever hacks.

My experience with this is in .NET, which has methods like readFile (which is async) and readFileSync.

.NET doesn't really need to provide two separate utility methods like this though, because you can use Task.wait to block until the async task is done.

File.ReadAllBytes/Text/Lines use synchronous underlying file API.

Their async variants call different OS APIs for asynchronous operation where available (Overlapped IO on Windows, on Linux it is specially scheduled (p)read and write calls).

A similar distinction applies to Socket where asynchronous calls use an internal epoll-based engine while synchronous ones are plain send/recv.

Generally speaking, in synchronous code there is no advantage to calling `.Wait()` or `.GetAwaiter().GetResult()` over synchronous APIs when such are offered, and if you can help it, it is best to update the code using them to be async too if your application is multi-threaded. Luckily it's quite easy in most situations unlike what HN public (that hates better languages like C#) would lead you to believe. But ff you do have to do block on waiting for a task, the impact on throughput is usually negligible if you do so within say threadpool worker - the implementation nowadays can cope with this very well and is more resilient to scenarios that used to be problematic.

I sometimes wonder whether this is really an optimization problem pretending to be a coloring problem. In some sense, the sync versions of blocking things are generally better in only one way: they can be more performant (run faster, use less memory, generate shorter code, etc). [0]. If a function can be implemented in async/await style, then ISTM the compiler could treat the sync variant as an automatically generated optimization instead of as a totally different (and differently colored) variant.

Of course, in languages like Rust with multiple colors of async code (single-threaded or multithreading-capable), this would get very messy.

[0] As a major caveat, synchronous code also enforces various state transitions much more efficiently. Want to prove that IO is done (in the sense that the user code is done with it) before closing a file? This is pretty easy in single threaded blocking code.

> And, it absolutely should not require creating two identical function definitions to get around the function coloring problem - that's completely indefensible.

Where do you see insanity like this?

Everywhere in the C# ecosystem. You’ll see things like x.Read() and x.ReadAsync().

That sounds more like a legacy problem than a problem with the async/await model in the abstract.

If you were designing a language from the ground up, why would you implement a synchronous read operation? I would just assume that all code written in the language will treat async the way that Haskell programmers treat IO and make all IO operations async no matter what.

There’s lot of programming models that don’t require async or it’s complexity. Not everything is a web server that needs to serve 100k requests.

Because Read and ReadAsync are usually meaningfully different. There is nothing wrong with that.

See https://news.ycombinator.com/item?id=41055328

This bifurcation is mostly a concern for the standard library. It’s not something you do this way in your regular application code.

Everywhere that hard function coloring exists where the language also supports synchronous calls that do the same thing (JS doesn't support sunchronous calls for lots of things and has only soft function coloring since async is sugar for Promises, so it has two reasons why that doesn't need to happen.)

Why have Json? We can always use binary to save a lot of space and bandwidth and the IDE will always compile it into plain text for us, why have underscore at the beginning of private variables? We can let the IDE do that, we even have long named functions instead of single letter ones? Most IDEs can read the jsdocs and give us a long description of what every function does, and I could go on and on. At the end it's a balance and subjective preferences of what you want to be immediately visible or something a bit more obscure (e.g. when you move your mouse over a variable)

> Why have Json? We can always use binary to save a lot of space and bandwidth and the IDE will always compile it into plain text for us

Yes, this is a great idea, and people would do it if there was widespread support for a binary structured format.

The difference between this incredibly ignorant sarcasm and my point is that IDEs already support the thing that I'm suggesting. You can already hover over a method and it'll give you information about the types of the arguments and return values that are specific to the call site.

> At the end it's a balance and subjective preferences

...and you completely missed the main point of my comment, which was not about what information to show, but avoiding duplication due to function coloring:

> And, it absolutely should not require creating two identical function definitions to get around the function coloring problem

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