Hacker News new | comments | show | ask | jobs | submit login
The Rust module system is too confusing (withoutboats.github.io)
103 points by AndrewDucker on Jan 11, 2017 | hide | past | web | favorite | 95 comments



In keeping w/ rust's philosophy of being 'c++ with marginally better tooling', I'm happy with the current setup. It's light years ahead of the perf overhead of #include + the pain of setting up linker args for libraries.

Are the keywords idiosyncratic? Maybe. Can a new user get it working in an hour and learn it in 2 days? Yes.

It would be cool if there were a polyglot build system that you could learn once and have the same expectations in every language. But there are downsides to this proposal (not least of which is the fact that when someone names a polyglot build tool, it's often NPM). I doubt the module system is the #1 or even the #5 thing people struggle with when learning rust.


I think the issue here is that it could be made simpler. If there's no extra value in the additional keywords and statements, then why have them?


> It's light years ahead of the perf overhead of #include + the pain of setting up linker args for libraries.

Sadly not yet.

My VC++ builds are still faster, because they can enjoy using binary libraries across projects, something that cargo doesn't yet support.

Also VS 2015 and the new VS 2017 do have quite a few improvements regarding the linker, incremental builder and C++ modules support.


> My VC++ builds are still faster, because they can enjoy using binary libraries across projects, something that cargo doesn't yet support.

This isn't anywhere near the top issue that I (or anyone else I know of) encounter with build performance in Rust. Dependent library builds are very parallelizable, so they tend to build quickly. Moreover, the build performance that matters in the day-to-day cycle is mostly rebuild performance, and the binary artifacts are cached in this case.

We could spend time adding a global cache of build artifacts, I guess, but all the time we'd spend working on this wouldn't impact my development velocity much at all. Incremental compilation, on the other hand, would.


Every time a new Rust release comes out, I try to update all the VSCode relevant plugins.

It takes me more than one hour on a core duo with 8 GB + HDD, while I occasionally see the same crates being compiled and get to do something else.

I could probably buy a new computer, as this one isn't something that one can easily parallelize, but why should I when my C++ builds are actually fast enough?

I am just an opinated Rust dabbler, please take my complaint as contributing feedback about what I see as one possible show stopper for Windows developers to adopt Rust, vs our current .NET + C++ workflow, in terms of productivity.

Thanks for Rust.


didn't realize #import had landed in msft tools! awesome.


Some information is available here.

https://blogs.msdn.microsoft.com/vcblog/2015/12/03/c-modules...

https://blogs.msdn.microsoft.com/vcblog/2016/02/11/compiler-...

There were also CppCon talks from both Google and Microsoft, but I cannot search for them now.


IMHO there are many obscure things about Rust for newbies, and its syntax is also less readable than that of Ada. This gives me high confidence that it has a bright future.

I'm not being sarcastic here, Rust seems to be a great language (definitely on my list to learn), I'm really just observing. Looking at the success and history of programming languages it seems to me that many if not most professional programmers want some obscurity, a desire that is often disguised as an apparent need for brevity which in reality plays no role with modern editors.

Maybe this makes sense, after all it's better to have a language that an incompetent boss or a marketing department cannot just pick up easily to 'roll their own solution'.


Which evidence do you see that points to obscurity or partial obscurity leading to success (or adoption, I can't tell which you're claiming)?


Not evidence, only subjective gut feelings, and I've had adoption in mind. But I'm hesitant to answer this question, because it will invariably lead to language flame-wars. Anyway, it seems to me that Algol68, Pascal, and Ada are less obscure than C and C++, but the latter are clearly more popular and have proven their worth over a long time.

At the same time, implicit-block type procedural languages like Visualbasic and Realbasic/Xojo are popular, but they do not get much love from professional programmers, even though they are maybe the least obscure among all imperative mainstream languages. LISPs are also an interesting case, S-expressions are among the least complicated and easiest to grasp syntax and CommonLisp offers practically everything a programmer could ever wish for (including multiple dispatch) but it never became very popular.

But maybe I'm wrong. For example, advanced Lisp macrology is definitely obscure, so that should count in favor of Lisp being more popular according to me 'hypothesis'. Haskell syntax is fairly easy, but monads are certainly obscure, yet Haskell does not seem very popular. Likewise, Python does not seem to be very obscure, it certainly isn't syntax-wise, and it's still very popular.

So I don't know, perhaps my assessment was premature. It almost certainly was. ;-) I've just always had this impression that many programmers prefer a certain amount of special trickery and shortcuts over clarity. But perhaps it's the availability of libraries what counts most in the end.


C is FAR less obscure than most of the languages you mention, ignoring things newbies generally don't need to worry about like standards, compiler implementations, memory alignment, virtual memory, etc.

I was able to learn C reasonably well as a child precisely because of how straightforward it is. You can reserve a block of memory. You can free it. You can get the address of a value. You can get the value from an address. It works in an extremely straightforward way, unlike most languages. To a child, programming in C feels like the computer is doing exactly what it was told to do and nothing else. It feels like you understand what is going on, even though your understanding is a very simplified model of what is actually going on.

Modern languages like C#, Javascript, Ruby... They are much harder to understand than C. The first time I saw a closure, I was completely dumbfounded. This doesn't make sense, a function is accessing a local variable of another function that has since been popped off the stack! What sorcery is this?? Even today things often confuse me, when I saw C# async/await for the first time I just couldn't understand how it can possibly work until I spent some time reading about it and I had been programming for decades by then including a decade in C#.


> This doesn't make sense, a function is accessing a local variable of another function that has since been popped off the stack! What sorcery is this??

This is an issue with learning a new language when you've already got your mind molded to a different one.

JS programmers have the exact opposite issue when learning C. Why can't we do this? Why must we worry about scopes for the stack? Wtf is the stack? I wonder what happens if I try to use this variabSEGMENTATION FAULT.

These languages generally are dealt with differently in one's mind, and trying to apply the mental model from language 1 to language 2 usually makes it feel harder than it really is.

I really could say the same about "it feels like the computer is doing exactly what you told it to do" about the other languages you listed. A crucial part is that you don't actually need to understand what the computer is doing under the hood to use it, especially in a higher level language. C is more like "you were forced to talk to the computer in its own language", whereas with JS/C#/etc you don't have to know what addresses and memory are. You just tell the computer what tasks you want done, and how to model them, and it does them.

So I'm very skeptical that the other modern languages you listed are harder to understand than C. They're just different.


The only problem is, I've used C# and JS way more in my life than C, and C wasn't even my first language (QBASIC was).

So unless learning C somehow causes permanent disability I will have to respectfully disagree.


Right, my point is that it's highly subjective and depends on how you approach things. I know programmers who have learned C later and they've always found the whole having-to-deal-with-memory thing an unnecessary distraction that they spend way too much time wrangling with, even after spending lots of time with C. I'm one of these; I have done lots of C programming but find languages like Python to be easier to learn.

C sort of does cause a disability (not really a disability, this is a useful skill!) in the sense that now you're actually thinking about how a language feature works in the hardware, which is not something you necessarily need to do for higher level languages. The moment you ignore all this it's likely that the language will make sense again. Of course, like I said, this is all subjective. The solution to "I can't use async/await because I don't understand how they work" is basically that you pretend that they're magic, and try to figure out the internals on the side. You need not understand how things work under the hood to use them, though it is an extremely valuable skill to know what C#/JS/etc end up doing at the lower level.

It's a sort of "ignorance is bliss" situation.

It varies from person-to-person though. It's not specific to programming either. When I was a physics student I personally would be easily able to define layers of abstraction in my mind and work within one layer, even if I didn't understand another -- you ignore how the other layer works and assume that it is magic (while simultaneously working to understand the other layer). One of my friends could not do this -- he had to understand rigorously how the theorems worked all the way down. As you can imagine, this required a lot of effort. It meant that he always had a thorough understanding of the topic at hand, but often meant that he spent a lot more time to understand something and had no middle ground to choose.

For me, this has carried over to programming. If I'm dealing with a language like C or C++ I will try to understand how everything works on the metal. When I first learned about C99 VLAs I spent an hour mucking with a debugger and inspecting the stack. When I realized that C++ had function-local initialized statics I spent many hours digging through C++ spec/implementations to understand how it worked (http://manishearth.github.io/blog/2015/06/26/adventures-in-s...). These are things at the same abstraction level as C/++ which I must understand to be able to use them.

But when I'm dealing with languages like JS, I can operate perfectly fine without knowing how they work. Indeed, when I first learned about generators, I was able to use them for quite a while before I learned how they work. I still want to know how things work (and generally dig into it), but it doesn't block me from proceeding if I don't.

This is not how everyone approaches languages. Like I said, it is subjective.


> This doesn't make sense, a function is accessing a local variable of another function that has since been popped off the stack!

That's only weird to you because C doesn't do it.

For someone starting in one of those languages, it simply makes sense that I can use any variable in scope. (Stack allocation? What is this sorcery you speak of?)


So you're saying that my problem is having basic computer knowledge?

Because stack allocation has nothing to do with C, C is not explicit about doing it (except alloca) just like most other languages, and other languages use it just like C does, including C# with its closures and async/await. It even has stackalloc.


Your problem is knowing how most C implementations work and trying to extrapolate that knowledge to other languages.

In C, a variable's lifetime is limited to the current function call. The natural implementation of C is to track both function calls and variables on stack structure with statically determined offsets. Thus, C has stack-allocated variables.

Since a Clojure variable's lifetime is not limited to the current function call, C's implementation details aren't relevant. Stack-allocated variables are a bizarre notion.


For some reason (as I didn't mention Clojure which I know nothing about) you are making the incorrect assumption that my confusion with certain features comes from trying to apply how another language works to a different language.

In reality it comes from trying to apply how that language works in normal cases (in the absence of those features), and the features requiring special compiler magic to work.

Yes if variable lifetime is as you describe in Clojure then that sentence doesn't make sense for Clojure.

As I've already told someone else, it is unlikely that learning C at some point in your life (not as my first language, not as the language I use professionaly, not even in my top 3 most used languages) permanently cripples your ability to understand other languages.


Yes but stack allocation is completely transparent in all languages except C. Well, almost, maybe all low level languages, the point still stands.

In any non-systems language you don't need to know (and knowing it doesn't help you with anything) this stack sorcery you're talking about.


How is stack allocation less transparent in C than in other languages? I don't understand this idea that the stack has something to do with C.

You can mess with the stack in C, you can also mess with the stack in C#. But you don't have to, and normally you don't. You use it in a completely transparent manner, not caring where the compiler decides to put your data.


> A function that accesses a local variable of a function that has since been popped off the stack

Here is where it's less transparent. In a language like javascript there is no concept of a stack so what's in the quote doesn't make any sense.


In the C language there is no "concept of a stack" either because the stack is not a language-level feature in most languages, it is a mechanic relevant to how your code is compiled / executed. And javascript engines, when executing JS, do use the stack. You can see a stack trace for your code in Chrome...

When it comes to stack allocation, in C this is the compiler's decision and in JS this is the execution engine's decision.

In JS, that quote makes perfect sense, and the answer is: the engine checks what can be safely put on the stack, and the stuff that is closed over is stored on the heap to avoid losing it when the function returns.


> I was able to learn C reasonably well as a child precisely because of how straightforward it is. You can reserve a block of memory. You can free it. You can get the address of a value. You can get the value from an address.

And everything function parameter is passed as value. In many 'advanced' languages, some things are passed by value, other by reference depending on the type, sometimes automatically, sometimes manually, it took me years to figure that out.

Same things for loops.

And I still have nightmares about some languages memory models: what is allocated where? what kind of allocation was performed on the object that this function returned, do I have to free it manually or will it disappear when I leave the scope? which scope? is it on the stack or is it the GC that takes care of it? when does it take care of it? should I call it manually?


With the amount of undefined behavior that C contains I find it hard to imagine that anyone would call it a straightforward language. Thinking in terms of the underlying hardware and memory can be misleading when one is confronted with things like signed integer overflow and TBAA.


A big problem is that many of us that used to be on the Algol/Pascal camp had this utopic idea that engineers care for quality and would choose tools that provide such support.

Wirth has a nice paper where he writes about the error of not doing any PR and thinking "build and they will come" would just work.

https://www.inf.ethz.ch/personal/wirth/Articles/Modula-Obero...

Check the "Conclusions and Reflections" chapter.


I share your gut feeling. It sometimes appears as if technologies that lack the opportunity for some to advance to magician status also lack a certain type of following.

That doesn't mean all technologies that have the necessary properties to allow some people to appear super human necessarily become popular. It just makes these technologies more sticky if they manage to somehow stay afloat for long enough.

I'm not sure whether or not these obscure sides of technologies are generally a bad thing. If a language provides opportunity for those who really understand it very deeply to come up with much better solutions, then that is a good thing. I would say this is the case with maths for instance, or rather with particular fields within maths.

But there are other much less favorable examples where it feels that these supposedly smart solutions shouldn't be necessary in the first place and getting even trivial things consistently right requires memorizing book length lists of rules and exceptions. CSS and C++ come to mind.


Actually Haskell strives to be unpopular. Their community has a nice motto for it, but at the moment it escapes me.


Avoid success at all costs. https://news.ycombinator.com/item?id=12056169


"Avoid success at all costs."


The fact that not every language on the planet is an implementation of Actionscript 3


I don't think the spread in difficulty between a non-obscured production programming language versus a highly obscured language falls within the range of a boss or marketing department.

I feel that what the general populace would require, if you wish to see programming languages more widespread, would be an ease of interface akin to a quality WYSIWYG editor, which companies have been working on for awhile. I would love to use such an editor myself, instead allocating my new cognitive savings for problem solving.

The gulf between WYSIWYG and the least-obscured / fewest constructs / best ergonomics / best developer UX / etc language still seems rather immense, even if you're thinking about Scratch. In Scratch you're dragging and dropping statements of logic, whereas in a WYSIWYG editor you're dragging and dropping elements of the page as you actually want it to look. The latter is much more declarative, and in range of what small business people want. I would argue that dragging and dropping for loops in Scratch really only helps for those who have keyboard difficulties. It's still a for loop.

I'd also add as a side point that obscurantism doesn't always mean bad ergonomics or bad UX. Sometimes it protects cognitive resources, and other times, when you are forced to dig, the bet for cognitive savings fails.


What's syntactically obscure about Rust?

I only knew(and liked) C reasonably well before Rust. And nothing felt obscure when I started learning it.

I can only remember not getting what `||` meant (in the context of defining a closure without args). The positional meaning of `||` and `&&` is the only thing, I can recall right now, that can be considered obscure syntactically (for C developers at least) . They should have gone with literal `and`/`or` for the operators IMHO.


I suppose it can get a little silly when you mix closures without arguments and the logical 'or' operator', e.g.:

    // prints 'true'
    println!("{}", true||(||true)()||(||true)());
Of course you wouldn't actually do this unless you're being intentionally obscure. Another favorite of mine:

    // prints '()'
    println!("{:?}", (||||||||||())()()()()());
But I can't recall ever running into such silly code, in practice the closure syntax and logical or do not lead to confusion (imho, ymmv).


> in practice the closure syntax and logical or do not lead to confusion (imho, ymmv).

That's true. But put your self in the mind of a C developer looking at Rust code for the first time:

     if a || b {
       println!("True");
     }
Cool.

Then:

     thread::spawn(|| println!("Hello from a thread!"););
What? What is the logical or doing there?

----

IIRC, there are also cases where you have to write `& &` instead of `&&` to not confuse the compiler. That's a design/practical issue.

Both those issues would have been avoided if literal `and`/`or` were used.

I find it interesting how the only thing that momentarily confused me, as a C developer, about Rust syntax, was caused by Rust authors not wanting to syntactically deviate too much from C.


The Rust module system is a little bit weird. As far as I can tell, this is the result of two things:

- 'use' statements are relative to the root of the crate, not the current module. To work around this, you can write 'use self::name' or 'use super::name' for relative imports. Annoying but no big deal.

- If you import a symbol into module 'a', it doesn't also get added to 'a::b'. I don't know why I keep expecting this.

Once I learned these two things, Rust imports were easy.

I'm not sure I agree with withoutboats' proposals. His chnages would make several obvious things work the first time, but at the expense of taking a simple, easy to explain rule and replacing it with something implicit and mysterious.

The bigger Rust learning curve issue is making friends with the borrow checker. I like the borrow checker. It has my back, even when I'm trying to write fast code that would be recklessly abusive of pointers in C. But I can't deny that it took me a week or two to make friends with the borrow checker.


'use' statements are relative to the root of the crate, not the current module. To work around this, you can write 'use self::name' or 'use super::name' for relative imports. Annoying but no big deal.

I'm writing an application. Inside main.rs I can write

  extern crate foo;
  use foo::Bar;
If I create a module and use the same crate, I need to write:

  extern crate foo;
  use self::foo::Bar;
This always surprises me and I never found anything explicit written on the Book. To me, it looks like a nice papercut to fix.


Why do you have an `extern crate foo` line inside a module that I'm assuming (because of the `self`) is part of crate foo? You shouldn't need to `extern crate` inside that crate itself.

One thing that might be confusing is that `main.rs` is the entry file of binary crates, while `lib.rs` is the entry file of library crates, and a project can contain both a binary and a library crate. The binary crate then does need to `extern crate` the library crate.

We've been working on a new version of the book, if you have time, I'd love if you would take a look at the new chapter on modules [1] and file PRs or issues on the repo [2] if it's still confusing or leaving you with unresolved questions!

[1] - http://rust-lang.github.io/book/ch07-00-modules.html [2] - https://github.com/rust-lang/book


I keep tripping over that as well. It makes the crate root feel special compared to other modules, and that's annoying because most people learning the language probably spend a lot of time in the crate root, writing simple toy programs.


What if I really do want the 'foo' crate to be inside the sub-module? If you want it in the crate root, you should put it in the crate root.


Sorry, I don't really grasp your comment. Maybe I can clarify what I'm trying to do.

My typical use case is importing definitions, for example an error type or enum from the crate, let's say something from tokio_core.

I'd like to use this enum both in main and in my module; from my (limited) experience, you need to extern crate tokio_core both in main and the module, then use the definition. In this case the syntax is different for somewhat obscure reasons.


Hmmmm, do you mean that you don't want to put all your `extern crate` statements in the root of your library? If you do that, you don't have to have the `self` when you use items from the crate within your modules. I've never wanted to put my `extern crate` statements within a module rather than the library crate root; can you elaborate on why you want to do that?


Hm, I'm still confused about what you're trying to do :-/ If you're trying to use something from tokio_core in your own crate, in neither place will `use self` do that, like you had in your first example... it would be `use tokio_core::foo::Bar`... and the `self` was the only difference between the binary and library, so I'm not sure what the paper cut is exactly.


Basically I start hacking on a project, then when finally something is working, I want to split it into a separate "something". Coming from the C++ world, I'd create a new cpp/h couple, maybe in its own subdir. I understand that the equivalent in Rust is creating a module.

I made a simple example with just two files: (In the meanwhile I realized that my first example was wrong :) https://github.com/lucaotta/rust_modules

Let's say that after my refactor, I've "moved" the crate import into the module since "logically" it belongs there. In this case the compilation fails if I don't use self::. But previously it was working in main.rs! And I have no idea why...


This is the "use starts at the crate root" thing. If you move the "extern crate", then the place it ends up in the module hierarchy is different, and so it breaks.

I always leave "extern crate" in the crate root; then it all Just Works.


The convention is to always keep `extern crate`s in the crate root. `use`s get moved around, but `extern crate`s stay put. Think of `extern crate` as if it were a crate-internal `pub use` (because that's kind of what it is!).


"I'm not sure I agree with withoitboats' proposals. His chnages would make several obvious things work the first time, but at the expense of taking a simple, easy to explain rule and replacing it with something implicit and mysterious."

Which is ironic, considering the premise is that the module system is "too confusing". Having never used Rust, the current rules - as explained by the author himself - seemed straightforward. For the proposed new rules, I'm confronted with two long paragraphs.

I didn't bother to read them. If the intent is to make the system less confusing, there should be a way to explain the new rules as tersely as the old ones.


A blog post proposal to the Rust community with a rough set of ideas need not fixate on itself being super easy to understand. That's for the RfC to do (we require a "how do we teach this" section on RfCs)

That being said, I do feel that the union of a confusing and simple system can often be a more confusing system so I'm wary of this proposal reducing complexity.


For me what's quite unnerving about `extern crate` is that the `extern` keyword has another function, that is to declare foreign functions [0]. `extern crate` on the other hand, is not an extension of `extern` but serves a completely different purpose.

0: https://doc.rust-lang.org/book/ffi.html


I fail to see how the usage is different? They both reference things that are 'external' eg. already compiled etc...


I mean if anything the syntax should me more specialised as you go into sub-keywords, which makes sense in this industry (e.g. ISO 8601). The problem is that `extern` seems to have been taken from C++ and extern crate is almost tacked on (or that's the impression I get). Comparing with other languages, Rust looks to be the only instance where two keywords are required to simply require a module/library, which sticks out to me.


No, you can also define `extern "C" fn foo() {}` with a body, which creates a function that can be called from C.


The main issue with Rust's module system is that your own modules and crates live in the same namespace. So if you have a `mylib/image.rs` file and you want to use the image crate then you can't without either renaming your `image.rs` or you alias the crate on import.

I really wish your own modules would require some relative import and be scoped within `mylib`. Eg you would do `use mylib::image::MyImage` and `use image::OtherImage` instead of `extern crate image as image_crate; use image::MyImage; use image_crate::OtherImage`.


So Rust essentially has the same design issue that Python had before PEP 328?


Not exactly; Python had the problem where `import foo` had two different meanings and there was no way of working around it. Rust still understands that crates are different, and will let you do `extern crate foo as bar` to avoid conflicts.


Correct me if I'm wrong, but I think the proposed implicit modules in the article would fix this issue. Instead of exposing mylib/image.rs via mod, you'd just import it as an 'implicit' module.

So you'd end up with `use image::MyImage` and `use self::MyImage`?


This was my experience, too. I had to keep checking other crates to see what was expected from me, and managed to finally understand through trial-and-error.

The problem with this is that I'm not likely to remember how modules work a few months after finishing a Rust project. I reckon core aspects of a language should be so simple that they don't need any work memorising them.


Mine too, or rather, for my first rust project I initially had all the code in main.rs and then I found it very difficult to split up the project into several source files. I think with some better documentation it wouldn't have been that hard.


I think it's the documentation. It took me a few tries to get everything I needed out of the Book to use my own modules, but then it was easy.

Although I still don't quite get how macro importing works. It feels like when you #[macro_use] on an extern crate you get all the macros implicitly everywhere without having to issue any use statements. This seems weird and I have yet to try to find an explanation of it. But I've got modules all over my Advent of Code solutions which use macros from nom without having any nom-related use statements.


Yeah, I hear you. I've always thought this, and honestly, I think the issue is that I've always found the module system _very_ intuitive, so it's been harder for me to connect with how people struggle to learn it.

http://rust-lang.github.io/book/ch07-00-modules.html is the second edition of the book's chapter on it, I think it's much better.

> This seems weird

Yes, that is how it works. Macros aren't in a namespace. Yes, it's weird. It's an artifact of history; eventually, it will be fixed.


> http://rust-lang.github.io/book/ch07-00-modules.html is the second edition of the book's chapter on it, I think it's much better.

It is better, yes, although I think it takes a while getting to the point in a few places.

Docs are something I'm interested in, so you might hear more from me through appropriate channels about this and that.

> Yes, that is how it works. Macros aren't in a namespace. Yes, it's weird. It's an artifact of history; eventually, it will be fixed.

I'm glad that I both got it right and that it's not necessarily going to stay that way. I don't know how much macros are going to proliferate in the future, but I don't want to find myself with macro naming collisions. I can certainly imagine some of nom's causing issues with other crates, and having to define a new crate within my tree just to contain them would be irritating. I assume that would work as a workaround, anyway.


Great. Please don't hesitate to reach out and or file issues or whatever, I really want to make this stuff good.

Basically, today you define macros with macro_rules!. This shipped in Rust 1.0 because we did not have the ability to invent and implement a more proper macro system, and didn't want to hold the whole language up on one thing. In the future, you'll write macros with a "macro" keyword, and macro_rules! will be deprecated, and "macro" macros will support namespacing, etc.


Is that "Macros 2.0", or something beyond that?


So here are some things the book chapter misses that are source of confusion elsewhere in this thread

- `extern crate` is logically a crate-internal magic `pub mod` or `pub use`

- You should usually put your `extern crate`s in the crate root

- Putting these two together, you can refer to crates as if they were toplevel modules.

This is one of the very common confusions I've seen.


Mind opening an issue with this in it? <3



> extern crate is like mod, but it declares an external crate dependency instead of a submodule.

Naive question: What the hell's the difference? Is a crate not a module? IMO, there shouldn't be a difference.

(EDIT for clarity)


`mod` makes things part of the current project, `extern crate` is for referencing other projects. The former is way tighter, bidirectional coupling, you won't have to deal with different versions of single source files in the same compilation unit, you can have mutually recursive references between modules within the same compilation unit, and it's relevant for the orphan rule.

In a nest module within the crate, you can use names defined in the modules containing you, transitively, but in a crate you naturally can't use names defined in other crates linking to you. It's really not the same kind of relationship.


crate is what gets released / distributed (i.e. a whole 'library', 'package', 'dependency', 'bundle'). Modules are single source files.


A binary is of course something different from a source file. But that's just a detail. The “user interface” should be the same for both, except maybe in the Makefile / Cargofile.


crates aren't binaries -- they're source bundles.


Oops, my bad. That makes the distinction even more baffling to me.


To be clear, `extern crate foo` refers to the compilation artifact, not the source of foo.


A crate is a compilation unit. A crate has a tree of modules.


The way I think of it is that a crate is a bundle of modules. Crates are quite free to make multiple modules public to be used by anything which is importing that crate.


Which should just be a module that makes all/some submodules available.


Rust module system is similar to C#: mod is namespace, extern is assembly reference. The difference here is that there is no separate "project" file, so all references to inner module files need to be described in the parent file.


FYI, /s/bare/bear


Well, maybe. Or you're viewing the article through your western cultural bias and missed the author's primary intent.


"bare with me" can only make sense if the author is asking us to remove our clothing along with him. I don't think that was his intent.

Telling him about the typo was meant as a courtesy to him, because I appreciate his post and want to help strengthen it in this small way.


you're assuming he wants to bare his body. maybe he wants to bare his soul.


I think it's possible to design a more intuitive system with less busywork:

1) For imports, the namespace hierarchy should have a one-to-one correspondence with the file and directory hierarchy.

2) For publishing code, instead of modules and Cargo, there would be one huge worldwide repository. You'd be able to freely import anything marked public, and the build system would cooperate with version control to make things work seamlessly.

Unfortunately it's probably too late for Rust to adopt such ideas. I wish some new language used them, though.


Given that crates.io has no namespaces, this is kinda sorta how this already works, I think. Or at least, I don't understand the distinction.


Well, you have two tools that can fetch stuff - git and cargo. In my preferred workflow there'd be only one tool. It would also work as a cloud filesystem, like p4fuse.


Cargo can use git, but it doesn't primarily. Crates are stored as tarballs on S3.


Right, I don't see why that's necessary. The whole world could be one big source control repository where each client keeps only their local changes. So e.g. if you want to make a local tweak to a third party library you're using, you 1) edit their file in your filesystem which is a transparent view into the world repo, 2) recompile your project.


That forces everyone to use git, which is not something we're interested in doing.


Agreed, it would force everyone to use the same VCS. I've lived in this kind of setup for years and I'm very happy with it, but point taken.


This matters less once we get good IDE support. E.g. "mod" should be inserted automatically when you create a new submodule, "use" will be inserted as necessary if you try to use something that is not in scope.

The other part is to have a set of conventions. Do I put "extern crate" in the root module or in the submodule that uses it? How do I order my use statements? Do I import just the module or each item in it? When the community settles on a standard way, IDEs can follow it.


Unless an IDE is part of the standard somehow I strongly disagree that "IDEs make it better" is a good argument for preserving a language feature that is confusing. Not everyone uses an IDE, and for certain low level systems programming kinds of things (you know, the things Rust wants to target) sometimes an IDE isn't available or is cumbersome to use.

That said I am a bit confused at the confusion. Rust is better than C++ in this regard, in my opinion, even if the system is a tad slower to build still.


Agreed. This should be fixed in the docs, diagnostics, and maybe by changing the language in a way withoutboats recommends, but we should not rely on folks having an IDE.


I'm hoping at some point rustfmt will order my use statements for me...


They should have looked at the good module system of OBJECT PASCAL (derived from MODULA). It is easy and allows all kinds of protections.

The main difference is that in this language a module always is one file, which consists of 2 parts. 1. INTERFACE (public) 2. IMPLEMENTATION (private) The way it is organized makes compilations also very fast.

USES only uses the public parts of the module. A LIBRARY is like crate in rust.

Sadly, this module system does not use private classes/types in public functions. But that would not be hard to add.

I have no idea what Rust tried to accomplish. Being used to Object pascal many other module systems seem primitive.


Actually that model came originally from USCD Pascal and was adopted by Apple for Object Pascal, but Borland did improved it quite a bit.

You forgot to mention, cyclic dependencies were allowed on implementation part.

Also later on, Delphi introduced packages, which are a set of units, with just some of them being public. Similar to the upcoming Java 9 package model.


How does this solve any of the problems listed in the article?


All you need to do is make `use` paths look absolute with a leading `::`, followed be either name a crate or `create` for the current crate.




Guidelines | FAQ | Support | API | Security | Lists | Bookmarklet | Legal | Apply to YC | Contact

Search: