1.26 has impl Trait, which is one of those things that really makes your life easier as a Rust developer. I've been using beta already with the new API I'm building just to get that feature, now on stable right before I'm actually thinking of deploying the API. Nice.

I also need to go and find all of my impl Trait TODO comments and get to work on cleaning those up! What a good day.

I should also say that while I haven't read the second edition of the book yet I am excited to have some new Rust-related content to read. The first edition of the book was a really eye-opening learning experience for me (both about computers and Rust and also about how to build a community and prioritize teaching) and I can only imagine what an improvement on that is like.

As always, happy to answer questions, provide context, etc.

  fn foo(x: i32) -> Box<Iterator<Item = i32>> {
      let iter = vec![1, 2, 3]
          .into_iter()
          .map(|x| x + 1);

      if x % 2 == 0 {
          Box::new(iter.filter(|x| x % 2 == 0))
      } else {
          Box::new(iter)
      }
  }

By contrast, if I returned a boxed trait, then calling the trait method requires a dynamic lookup to find the method on the boxed object, and then jumping to that function (dynamic dispatch). In this example, `iter.map(..)` and `iter.filter(..)` return two different implementations of the Iterator trait, so dynamic dispatch is required.

In general, if your function returns multiple possible implementations of a given trait, then the compiler cannot know where the trait methods will be statically, so it is impossible to do static dispatch. Since impl Trait wants to guarantee static dispatch, it requires that only one possible implementation of the trait be returned.

The offset of the function pointers is always statically known for a given trait/interface type, it's just the actual vtable instance that may not be known, ie. the concrete type implementing that trait/interface. A statically known vtable instance that can be inlined/monomorphized is static dispatch, and if it's not known at compile-time it must be dynamically dispatched.

"calling the trait method requires a dynamic lookup to find the method on the boxed object"

It sounds like all you want to say is

"calling the trait method requires a dynamic lookup to find [the vtable instance, which is then used to find] the method on the boxed object"

> then the function pointer will always be in the same place on the object in memory (static dispatch)

As I said, static vs. dynamic dispatch is about knowledge of the vtable instance, not about the offset into the object or the vtable. All of the offsets are always known statically, it's merely what you're indexing into that may or may not be known statically.

Maybe I'm being pedantic, but I've found that there's a lot of misunderstanding surrounding static vs. dynamic dispatch.

There is some discussion about it possibly being sugar for an anonymous enum in the future, but that’s not what it is right now.

In Rust (most languages), by default the compiler needs to set aside space on the stack for each return value. So it needs a constantly known size (and shape) to create the slot on the stack. You need to flip to dynamic dispatch, ie a pointer to an object (Java's default), that will be placed on the stack as a reference to the unknown size/shape of the thing at the end of the pointer when the size/shape is unknown. A pointer always has a constant size on the stack.

In this example, `impl Trait` is just saying I want the compiler to figure out the size/shape of the thing being returned for me, and allocate that to the stack at the call site of the function. What this means is that even with `impl Trait` you must return a thing that has the same size/shape.

Steve's answer mentions a common pattern used to create constant size/shape by using an enum for the wrapper type to return two different types on the stack from the function. The only other option is to put something with unknown size behind a pointer, ie Box<Trait> or &Trait, and thus pay the expense of dynamic dispatch.

There’s a crate on crates.io for it if you want to use it for something.

Is there anywhere I can get a quick recap of major features Rust is planning to eventually maybe implement, and their state? I mean major features like NLL, impl trait, etc.

IIRC: NLL are nightly already, const generics in planning stage, and what happened to CTFE? For us not in the know, a sneak peek on what's coming/being discussed is very exciting, but browsing the issue/RFC tracker is sometimes a PITA and it's hard to keep up to date, especially after getting used to the workarounds.

I mean, just yesterday I had to do some weird stuff to a for loop in order to iterate over all u8s in a cleanish way.

Lovely, lovely work. I'm especially excited to see how clever the ref/ref-mut `match` inferring is. If it's reliable, that's gonna remove quite a bit of friction for newcomers. So cool!

Being able to return anonymous trait impls from inside functions could eliminate a lot of what seems like boilerplate structs/impls from Rust code. As an example, the code in futures-util that adds combinators to a Future defines a type (Then, Fuse, Map, etc) for each combinator function. With those functions now able to use 'impl Future<...>' as the return type, being able to actually type 'return impl Future<...>' could make code like that a lot less cluttered.

While I'm sure it won't mess anyone up, the range for the i128 is hard to interpret. It looks like -xxxxx - xxxxxx but with the extreme number of digits it looks like two negative numbers or a subtraction problem.

[edit: u128 -> i128]

Is the non-lexical lifetime improvements work locked to a particular release yet?

Also, now that the async/await RFC has been merged, is its implementation in nightly or stable going to be squeezed in for the 2018 roadmap plans?

As for non-lexical lifetimes, there's lots that's been implemented but much of it is still experimental; follow Niko Matsakis' blog series at http://smallcultfollowing.com/babysteps/blog/2018/04/27/an-a... to stay up to date with what's happening.

Question: Is there any way to preview what the book's typesetting looks like, since there's praise in the release note?

It shows off Chapter 3, and yes, it really looks great.

Rust promises that existing versions of crates will build and run in the future, assuming the crate is well-behaved and doesn't do anything illegal with unsafe code. That's part of Rust's general stability guarantee.

Maybe "blessed to be maintained" means crates get ongoing critical security fixes? Thanks to Rust, for most crates that's a very low-probability concern. (Obvious exceptions for features like HTTP and TLS that contain their own security decisions.)

Maybe you mean that all kinds of bugs will continue to be fixed and the quality of the crate will keep increasing? I don't think any languages really give you that; they all have standard library features that are effectively end-of-life. A lot of application developers don't even WANT such fixes since there's always a risk of breaking previously-working applications.

So I think it would make sense for the Rust community to commit to a subset of crates for ongoing maintenance, but for probably the majority of crates you could just keep using the exact same version for the next five years with no worries.

It's totally fine to decide to make the trade off, but it's just frustrating to not have the downside acknowledged.

Adopting crates into the stdlib would make stdlib and the crate depend on each other, which is not a nice scenario. Also having certain "core"-functionality be dependent on a 6wk release cycle is not great for stuff that is not good once it's set in stone (aka released on stable).

Real core functionality, bare bones stuff like parsing of Rust itself, I/O and TCP/UDP connectivity, which provide an unlikely to ever change framework for crates to build upon rightly has its place in std; e.g. convenience methods for downloading (like what reqwest provides) OTOH have to stay flexible to adapt to the real world.

Cause it sounds like a strong commitment here.

Though we are calling them “editions” instead of “epochs” now.

All that said, Rust definitely errs on the side of preferring to put things in 3rd party crates instead of stdlib, even for things that are very common to put in std for other languages (e.g. random number generation).

- HTTP client

- CSV parser/generator

I know Hyper and rust-csv are popular. But having an stdlib that's much more feature complete would be great.

Developers have different needs. Some value stability, some value bleeding edge features. Trying to put libraries in the standard library and freezing their interface is really tricky to balance.

Though the ecosystem is still young, the long term story for "batteries included" in Rust is going to be a rich ecosystem in Cargo, not a rich standard library.

So someone who wants batteries included could add only std-ext as a dependency and get hyper as std_ext::http, regex as std_ext::regex, rust-csv as std_ext::csv and such to avoid needing awareness of the entire ecosystem when first starting out. Seasoned Rust developers would probably continue pulling in dependencies directly, but it might improve the experience for new Rust developers to have everything a 'use' statement away without needing to go look for it.

Also, some suggested metapackages/bundles wouldn’t hurt for newbies, like a set of crates for developing command line tools, for example.

Something like this: https://marketplace.visualstudio.com/

What if a 'winner' today is a loser in a year? What if we come up with a new approach to solving a problem that requires a breaking change, or a new crate?

Would someone be inclined to try to improve the state of HTTP given a good enough version in std? Would we be ok with discouraging that sort of competitive approach?

To be honest, all I see are downsides to having a huge std lib. The benefit seems to be that there isn't an obvious, de facto choice for what crates to use. But I think that's a problem better solved by crates.io.

My impression is that many of those who are asking for Rust's stdlib to grow are also/actually asking "please make it really easy for me to use these APIs that I care about," to which I would respond "it's OK, code can be easy to reuse even if it's not in the stdlib," "try cargo," and "crates.io needs to continue improving on discoverability."

EDIT: also, hi!

I think we're likely on the same page. The desire to make writing an HTTP server that much easier by providing a quick-to-use solution is entirely reasonable.

I just don't believe the solution is some 'sanctioned', permanent addition to std.

Better to be solved in crates.io.

That way libraries can coexist, but new developers have a single doc location to go to to find really common usages.

It might be nice to have autogenerated docs about the most used soltuions, but I guess the rust cook book sort of fills that niche.

Incidentally you might like the phf crate, depending on your needs.

'const fn' seems like a red herring -- I don't want to write const functions, because I don't want to write code to initialize data structures at all. I want to write representations of data structures...

const fn isn't a red herring; you won't be writing const fns, you'll be using them to do the actual initialization. If maplit would use them internally, for example.

Which charity/charities?

Source: I've volunteered for them in the past as an instructor.

I have no idea how big the donations will be, but we're giving it a shot!

impl Trait is HUGE. And there's tons of other stuff too. This must be the biggest single release since 1.0.

Out of curiosity, why was the (or an alternative) choice not to make the compiler understand that the 0..256 was not inclusive, and somehow correct the literal value to do what's intended? Would that have been unusually complicated or?

Edit: Overall, still an amazing release, this was just the bit I'm curious about :) Great work by the whole Rust team/community

[1] https://groups.google.com/forum/#!msg/golang-nuts/7J8FY07dkW...

The community is amazing, and I actually understand all these features that were released I've run into about half of the issues they fix already.

Rust is coming along very very nicely.

I haven't used it enough to have much more to say -- I've found everything pretty ergonomic so far (especially for a C/C++-tier language), I was most frequently confused when thinking of the most idiomatic way of doing something, but that's remedied by reading more (the rust book first/second edition, the rust cookbook). This should change over the coming weeks.

This isn't a particularly useful comment, but I chose Rust over Common Lisp recently for this new project, and I've found the std library's google-ability to be excellent for rust -- very few pages about steel have come up so far ("result rust" in DDG brings up rustlang related links). When I explored CL, I did not find that to be the case, but maybe I just didn't know where to look -- hyperspec is close but it is a terrible document to navigate through, and the 90s graphics didn't help (though they were nostalgic). Rust documentation is very often concise, well structured, and passably beautiful. I was also pleased with the Abstract Data Type solution in rust -- tagged unions. Some code:

    #[derive(Debug)]
    pub enum ConfigLoadError {
        EmptyFilePath,
        IO(IOError),
        TomlParse(TomlError)
    }

http://play.rust-lang.org/?gist=4f74d3dcee0031e99cb99bb54da5...

Concerning keyword args as I remember them from Python you would probably have to hack something together with an Into<Option<HashMap<some_type_for_arg_names, some_enum_with_variants_containing_acceptable_types>>>

Concerning "named paramters" I think you would have to apply some of the same trickery in order to be able when calling the fn to leave out args or give them in a different order than specified in the fn header.

Or what I've sometimes seen written was (e.g. for configuration passing) structs created with Option<some_type> that were then passed to one or more functions which in turn get the values (named params/default args if you will) from that "object", being able to pick and choose the appropriate values to get in a given function/method.

Keep it up Rust team. The language is incredible! Really my only daily complaint is IDE support is still abysmally slow, in both IntelliJ and VSCode.

This and not being able to do paramterized array sizes for things like SoA, AoSoA where the two things that I feel like were missing from Rust. Really happy to see the first landing(and I understand work is going on for the second).

But I needed this yesterday!

Seriously though, this is an amazing release and so much stuff in here I've been looking forward to for ages. impl Trait is going to change the way I write Rust.

Personally, not a fan of the match change. But then I was already not a fan of autoderef in method calls.

    let example: (String, String, String) = ("ref".to_string(), "to".to_string(), "ref".to_string());
   
    let example: (&str, &str, &str) = match &example {
       (ref1, to, ref2) => (ref1, to, ref2),
    };

https://play.rust-lang.org/?gist=e37f9b31cc5e5c7b9d19c6b0a4c...

For field access/method calls, autoderef is a bigger convenience because we don't have the C++ -> operator, but I think I'd have preferred a syntax change here over the current behavior.

Deref coercion makes a &Box<T> behave like a &T (removing a level of indirection). Default binding modes only make a &(T, U) behave like a (&T, &U).

I've idly wondered whether it would have been possible to replace deref coercions with something like this. Making Box<T> behave like &T kinda works but loses you the ability to control `&T` vs `&mut T`, but maybe `x.y` where `x: &T` could "pass the reference on" giving you a `&U`.

    fn foo(s: &[char]) {
        match s {
            ['a', 'b'] => (),
            [.. 'b', 'c'] => (),
            _ => (),
        }
    }

    some_collection.windows(2).filter(|[a,b]|a==b).map(|[a, _] |a).collect();

Maybe there has to be some special case handling for this pattern to be valid?

EDIT: I didn't read closely enough. Only a single type is allowed, so the traditional existential type construct ("trait objects") are still needed.

Would the book be updated as new features are added to Rust? I see some useful things being incorporated slowly into the language...

Work on the "2018 edition", which is the next version after "second edition", is just starting. It will be getting updates as new stuff lands, though there may be a bit of lag. In general, docs are going to be a bit weird up to the Rust 2018 release; it's all coming together, but slower at first, faster at the end.

(This means that, as of right this moment, there aren't great docs for impl Trait. I'm working on them right now.)

By the way, how is the progress of supporting XDG base directory spec for rustc and cargo?

One iterator simply returns the value and increments, and the other needs to apply the filter first and potentially advance several times.

Rust on the other hand is targeted more towards developers that want C-like low-level control along with safety against shooting themselves in the foot.

The former audience is probably larger than the latter. But popularity isn't everything (JavaScript wins that contest ;)). The important thing is Rust is doing an amazing job in an area that hasn't seen much love.

Rust hits the sweet spot of not being a pain in my ass all the time.

Yep, checking in. I want to write libraries that work on Windows, Linux, OSx, iOS, and Android that expose a C api but without having to write any C.

I know a bit of C, but not enough to feel like I can effectively use it to build the things I can build with Rust.

I love what the Foreward [1] in the Rust Book has to say about this:

"Traditionally, this realm of programming is seen as arcane, accessible only to a select few who have devoted the necessary years learning to avoid its infamous pitfalls. And even those who practice it do so with caution, lest their code be open to exploits, crashes, or corruption.

Rust breaks down these barriers by eliminating the old pitfalls and providing a friendly, polished set of tools to help you along the way."

[1] https://doc.rust-lang.org/book/second-edition/foreword.html

That you see them as being so different languages reinforces my premise above; they're good at different things, so comparing them doesn't always make a ton of sense.

The word "systems" is increasingly relegated to a smaller fraction of the codespace than used to be; one wouldn't have considered building a high frequency trading system or a call handling system in a non C/C++ language in the mid 90's, but Java and Erlang get the job done well enough.

As always Alan Perlis said it best (in his "epigrams of programming"): A programming language is low level when its programs require attention to the irrelevant!

https://github.com/google/gvisor

a) In terms of memory safety, Go is not memory safe in the presence of data races, and Go does not prevent data races at compile time.

On top of this Go does not enable ASLR on most OS's. That means that when Go loads code from other languages, such as C/C++, memory safety issues in those languages are extremely easy to exploit relative to in a language like Rust, which enables tons of mitigation techniques by default.

b) More loosely, Rust has a more expressive type system. It is, in my experience, much simpler to enforce constraints in a 'type driven' way. In my opinion, this leads to safer software.

As an example of (b) I have written authentication code that encodes the authentication protocol's state machine into the Rust type system. What this means is that it is impossible to jump between two states in an undefined way. Beyond that, because of Rust's affine type system, it is impossible to reference invalidated states.

For authentication code, especially when you add complex stateful transitions such as rate limiting, whitelisting, etc, this is an extremely effective way to reason about your security critical code.

I think there is a case to be made that there is a real, significant difference between the languages regarding security.

You could also make an argument about compile-time guarantees more generally.

I'm not sure it's really a great argument, but you could make it. I think the parent's statement that it's only Go because it's made by Google is demonstrably false.

Google can make money in one way and still provide real value in others, and that’s what they (and all of Go’s contributors) have done with Golang.

It's rational to take these factors into account, but they don't reflect on the merits of the language itself, and aren't necessarily transferable to other people choosing programming languages.

It takes a long time for a language to build momentum and a user base. Python was just starting to get popular when I graduated from college in 2005, and it was already 16 years old at the time.

I think you can do that in Rust too (post 1.0). What's more impressive is that canonical go code from five years ago is still canonical.

Most apps out there are extremely serviceable with a language environment that runs up to 2x slower than what is possible with Rust. Youtube, edX, reddit, coursera all run on python, Facebook on PHP/Javascript, WhatsApp on Erlang.

In exchange for ceding low-level control, these languages provide a frictionless approach to evolving a system. You get dynamic features that are simply wonderful for creativity. Javascript is a blot on the landscape, but look at the effortlessness of d3.js.

GC is wonderful and does not gets in the way for most apps (from mobile to enterprise). Any time spent thinking about lifetimes sucks the fun out of coding. Lifetimes are fantastic for concurrent programming, no doubt, but there are simple patterns in Go that work well in practice.

Lightweight threads remove another point of friction; they allow you to model the concurrency inherent in a problem without much trouble. I'd prefer Go to get more of Erlang's failure handling and signal delivery mechanisms.

Go is a middling language, but its libraries and ecosystem are solid and have a coherent feel. They work out of the box without having to consult StackOverflow a zillion times.

The language I would love to have is Swift retrofitted with Erlang's process system.

Rust improvements like NLL will hopefully reduce the costs. I think we will discover more ways to leverage the benefits, over time. However, I also think it might be interesting to let people opt into a Rust dialect that hides lifetime issues, e.g. using a lot of implicit Rcs and (Ref)Cells.

Go also hits the sweet spot for CLI apps, in my opinion. The error handling is obtrusive and annoying otherwise, but for command line apps where you're just aborting whenever you hit any kind of snag, it's not a significant pain point.

I think this is a pretty major piece as well. Go was introduced many years earlier, backed by Google marketing and had strong HTTP services as a day one feature; it was designed for probably the most popular use case by perhaps the most influential fount of new tech. Given all that has Go really done all that well? Has it gone much beyond network services and a couple other niches (Docker/K8s etc?) It's not really displacing C/C++ in 'systems' use cases. It's not a go-to language for Machine Learning. The runtime+GC obviates most embedded work. You don't see any meaningful uptake of Go among Google's peers; Apple, Microsoft, Oracle, etc. I wonder just how important Go really is.

I don't think it was ever intended to be important in those terms, however. It was designed primarily to solve specific sets of problems at Google, but I don't think any sights were set on the C, Java or other related language worlds at large. From that perspective, I would argue that Go's actually been fairly successful.

I'd argue the Rust team is much more eager to be a real disrupter. I think in that sense, they're succeeding in ways and have not yet achieved success in others.

My intuition is that the only languages that have grown faster are those that were blessed as "native" for a popular platform. For it's age it seems to be doing really really well.

But given Go's mix of advantages and disadvantages, should we expect it to be doing better? I doubt it.

Still to be seen if it becomes a Ruby or a Java, though.