RustConf 2019 - The Symbiotic Relationship of C++ and Rust by Isabella Muerte

[Music] all right cool so as was briefly mentioned we're gonna talk about C++ and rest today so just so you all know who I am I missing Marte and I'm a C++ bruja I do a lot of dark magic stuff with C++ if you know me personally than you know that I do some really cursed things I'm an aspirant row station so I do do a bit of rust on the side not my day job also don't really contribute to a lot of projects that's because I'm busy because as of lately I've become a bit of a sea make war criminal so um I do some really disgusting things in seeming as of late you could also make the argument that I'm not a super sports programmer anymore I'm a seeming program that just happens to those people see what's plus I promised not to talk about see make today I did that at the rusco last year and at one point someone just kind of walked away a little little like depersonalized disassociating like I just wish I didn't know any of what you just told me and then Michael made this tweet the other day he it's been zero days since I had a truly cursed idea and that's pretty accurate representation I care a lot about developer workflows build tools making it's that you have to type lessee or computer cuz the more we type the heart higher a chance of having arthritis as we get older increases I also currently hold the record for most papers submitted to a single C++ sustainers meeting um that was completely by accident my name was on 20 papers I don't think anyone's gonna break that anytime soon so just just to give you an idea that I do care abouts people supposed a little bit I started teach myself see post post about 10 years ago by writing the build system don't learn how to program but I write in the build system if you have a friend that is like I'm thinking of writing a build system tell them not to care about your friends and the people around you I've been pay attention to rest for a while as Steve kind of made made mention of 0.5 and the kind of the syntax of you know the the old tilde T back when tilde T and at T were still a thing this was before the borrowed checker and when I think everything was still either like equivalent to a unique pointer or a shared pointer in this equals plus side and iterators were still more Ruby like so the the current stream iterator implementation that has been used since you know forever wasn't really a thing so that's my Twitter that's my github yes it is slurps mad rips I can go into the story of why I chose that username in 2012 but let's not right now and I also just want to set up some some boundaries real quick so you know any questions let's look until after the talk if we don't have time for questions you can speak to me in person outside I won't actually sit off to the side here I'll actually physically walk out just so that we can give more people space up here for the next talk and lastly you can always tweet a question to me with that hashtag 1 2 3 you got a CPP I and I actually checked this hashtag every couple of every couple of weeks because you know maybe you're watching this at home maybe you had a question that you wanted to ask me forgot about it then remembered it on the way home after the conference this allows you to ask that question I will respond to it you can also at me but by using this hashtag other people can also see what questions you yourselves have asked so a couple extra talks that I suggest all of you go and watch at some point after this conference and after this talks to you can kind of get a better idea we only have 30 minutes obviously there's the elsewhere memory talk by Neil Douglas I'm from ACC u 2019 Jen shivers talk on JavaScript considered useful and then the tragedy of systemd by Ben o rice I'm pretty sure I just murdered his first name there but these these three talks I've been watching pretty pretty regularly because they they cover a wide variety of different things from the super suppose abstract machine to community related things as well as even standardization in the case of Jen's talk and we're going to talk a little bit about each of the things that is that are in these talks but in reference to super supposin dress today so as I said you know why are we here so I think they're gonna be super so much gonna be living side by side for quite a long time if only because contracts with you know various industries exist there are people that are still running seek until 2050 on military hardware so if she's gonna live that long C++ will definitely live as long because currently the C Standards Committee Charter says that they are to keep basically in lockstep with C++ and to make sure that C stays compatible as C++ rather than what used to be the other way around Russ also is not going anywhere I think it has too much momentum at this point it is technically a 13 year old language so you know it's it's old enough to curse at me and tell me I'm bad at counter-strike online C++ is kind of like the 40 year old burned-out person that used to play quake in 1993 or whatever so you know neither of us are going anywhere anytime soon and we might as well work together to learn from each other's mistakes there's a lot of stuff involved with tooling with optimizations that we can learn from and you know while be honest use to creative C++ might say other languages are copying C++ there are people on the Standards Committee at first super suppose that are looking at what Russ does for optimizations for language futures and we are borrowing from them I've submitted quite a few papers in regarding that so just to give you an idea of like how similar languages are we've got you know a lot of stuff that is similar but our terminology is starting to drift kind of like you know how you know the Romance language is drifted and if you speak Spanish you can kind of understand Italian and if you speak a tell you can kind of understand Spanish you know there's a lot of similarities there and we're both kind of trapped trying to express high-level concepts for machine code and rust doesn't have an abstract machine C++ does and our abstract machine is basically the pdp-11 and if something can't meet that then it's not really an abstract machine it's kind of a shame but rust does have to meet a lot of the stuff that C++ does because by using LLVM you're stuck with our memory model and if in the future and Vidya says we'll adopt the rust memory model over C++ then we'll have to follow you know your direction of things but I don't think that's gonna be happening time soon unfortunately or fortunately so here's some code differences here so you know russ has let we have auto I didn't put Auto Const because you don't want an auto our value reference and that's let's not you know what let's just not get into that part of the language it's kind of a landmine russ has the turbot fish we have both the apologize I used Furyk hose that's why it looks like a diamond there as well as the scope template syntax the the form of that we used less nowadays we're relaxing type name and its usage and it's making write a generic code easier also means that this kind of you know call scope template thing is disappearing the if let's some or if let you know some value expression is kind of equivalent if Auto X equals some boolean expression and moving into more literals in C++ xx we still have to write using this stupid macro from C's C stood int in 64 underscore C to get an actual int 6040 whereas in 23 do paper I'm writing we can we will actually able to write the same thing that rust has and that is actually a library feature a language feature because we're so cursed we said hey what if anyone could just write whatever suffix literal they wanted for a given built-in tight and someone said yeah that sounds cool our integer separators are a bit different rust has borrowed from a variety of the languages Python Ruby I think Perl maybe but a lot of people are moving in this direction of you know that using underscores as an digit separator we chose the single quote in C++ because econometrics this the choice of a period or comma without us having to get into localization issues I personally believe that the C++ one is a little better and I've also seen people writing integers out in actual like papers using the C++ syntax instead of the underscored version I think in academic papers you'll see that C++ form more even if the paper has nothing to do with C++ both Wilson Russ can overload some operators I found out last night that you can over overload the not operator in rust and we can also do that in C++ so hey we both have a really bad decision that's great rust moves are equivalent to a new concept that we're trying to try out in C++ which is called relocation our moves are kind of just a tag on the type system so when you have an r-value reference and you've moved something into a function that does not mean that the data has been moved from where as in rust moving from something implies destruction relocation might be an optimization that comes in the future we're still trying to even figure out the basics of antics of it it's gonna be a long road we probably won't see it in actual practice until 26 or 29 rust has working groups we have study groups they're both kind of the same anyone can participate in a study group in C++ anyone can participate in the working group you still to book you know approach both of good faith arguments and that's a like I said we don't have enough time unfortunately so apologies so also technically speaking this code that you see here this could be valid C++ or rest code those of you that are familiar with plus plus might have figured out already what I'm doing here which is you just start define let to auto and you're on your way I already discussed the memory model stuff and Neil's talk about the abstract machine is very interesting if it's actually about two hours but it is extremely interesting talk because it kind of gives you an idea of where the hardware that we currently use today comes from where it's going to and the limitations that we have to deal with because you know you could have a high level language that could do everything but if you know the CPU is gonna be flipping bits behind your back and you don't know about it that's gonna cause problems for you of course we also have our differences we're not going to talk about defaults okay we already know about it's like a dead mean right like rewrite it in rust dead meme talking about cost as default and mutability also a dead meme I don't want to talk about it let's talk about lifetime semantics we're talking about concepts and traits because they're very similar but very different this is just what I'm calling this right now the execution context boundary this isn't a thing that we have term for in either community yet but it is something that's gonna be coming up because of changes in C++ 20 so Russ lifetime semantics as I'm sure you're all aware it's baked into the language otherwise you wouldn't have a you know lifetime you know syntax to represent it most of the time this this concept of lifetime ownership and stuff like that can be mapped to existing api's from foreign languages so see if you're trying to call into C++ in some way and you figured out how to generate the correct symbol for it sure even there and custom semantics do break down though when you get into stuff like objective-c or OpenCL and yes from an optimization perspective you do not want to always be retaining and releasing these but at the same time sometimes it's nice to just take someone's really garbage objective-c code and then to just copy it into your own code and not have to change as much C++ lifetime semantics we don't have any we literally do not and everything involving unique pointers shared pointer all of this stuff has is defined by the library portion of the standard so the language doesn't have a concept of a unique pointer of ownership and releasing ownership of you know incremental counts and dereference counts and all that other stuff or sorry decrement accounts but as so as I said everything's library to find mostly obviously value semantics destructors and stuff like that those are at the language level both languages have this constant of D res I'm not gonna use are aii because one it's a terrible terrible acronym it's impossible pronounced right it sounds like a bread if you just say it out loud whereas d res you can make a joke about Tron and everyone's gonna understand it like immediately right and yes I know a drop does not imply a destructor it could be a scope based resource but de res de sounds cooler as an example retain pointer this is a type I've been working on so retain pointer I first wrote it the proposal for it in a night in 2016 because this is a type that is meant to you know work with capi is like you know open Seattle or Objective C because Objective C is AC runtime it's meant to work with you know calm and direct decks and some parts of the the mono framework web browsers have implementations of retained pointer inside of them Safari specifically inside of the WebKit tool framework which is namespace as WTF has a type called retain pointer as it turns out I did not know this when I wrote the paper and then also it's useful for implementing async API it's basically stood future stood shared pointer stood weak pointer it's an exception pointer and we still retain pointer itself all of these can be implemented with retained pointer you know on the rough side if you had an equivalent to retain pointer you would be able to implement both RC and arc in terms of a retain pointers this is a very low-level type and introduces this concept of adoption right we have we have the concept of extending a lifetime of a type we had the concept of ownership of a type but we do not have a concept of a value has come in from some boundary that we do not know where it might come from exactly we just know that it has come in from a function and we want to be able to use that tight for a brief period and eventually kick it out of our house so kind of like adoption but not maybe not the best term in that case I guess so so this this type is there's a someone on Twitter whose name is our Berger ceman he is a bit of a firebrand and in that he disagrees with everything that c++ company does and says this is just over complicated I don't care about this in either should you but after I presented this the subjective version of retain pointer in 2018 last year he came up to me and said I've implemented this six times in my code base I'm replacing it with this and if Arvid says this is a good idea for this people suppose standard library to have then maybe you're onto something so let's talk about resource concepts for quick so rust rates are maximally constrained right if if a type does not mention what traits it uses you can't call any member functions on that right whereas in C++ they're minimally constraining C++ says this type has to meet the basics of this interface but other than that go hog-wild I don't care if this function doesn't exist if I have to do a lookup later you might get an error there and so more work has to go into a concept to make sure that the minimum interface is being met and we're gonna also discuss briefly so they are now I had to add this literally five minutes ago special members which are constructors destructors copy constructors assignment or now follow the best fit model as of Cologne which was back in June and as an example here here's a cost expert optional implementation where the destructor that is trivially defaulted there will be used if the given T which is destructible is also trivially destructible if it is not then we have to reset the optional on destruction that does that make sense like I know this it's a mouthful but the semantics for this are basically why we did this because we can use this on member functions as well in C++ so let's look at using a concept so this is this is some garbage code here and I apologize but this is just the best way I was able to implement this and this is basically to say if a type has an element type def or if it has a pointer type def i want to get that out of it and use that as a storage value and so this is a slightly regular type because unfortunately we have the concept of a regular and semi regular type but for that to be true something has to be copyable not only movable as a minimum we also decided at cologne to change all of these names to a snake case instead of the upper cased form and I didn't feel relighting any of this code so you're just gonna have to deal with it so here's a pointer like type this is for our smart pointer interfaces right so you can get it you can cast it to a bowl explicitly you can reset it you can reset it with an instance of the pointer type internally hence the pointer type of T which we saw two slides up we're not gonna get into this explicitly here but you'll also notice on this line right here we're checking to see if you can call the arrow operator directly as a member function rather than calling the arrow because that's a thing we can also do in C++ isn't that a nightmare but here's here's a handle right this handle can implement any kind of ownership model as long as that ownership is defined by this pointer like storage type and as an example here we can have a unique handle we can have a shared handle we can have a retained handle we can also have a viewed handle and you wouldn't hold this as a member inside of the class you would actually inherit from this in C++ this is basically a mixin type and as an example if we use the Android NDK as an example here we have a simple enum class with an orientation and here's a configuration type now there's a lot of code here the important part here is that we just inherit from it and in our constructor we that is copying we have to call this a configuration copy thing use this other thing called out pointer let's not get into that part that's not what matters what matters though is you'll notice this class does a whole bunch of stuff you can reset with it you can cast a tooling you can check to see if it is a valid configuration or not that is I think really powerful and C++ is that we do have the ability to have mix-ins that also then expand the lifetime semantics of whatever it is trying to make C's needs to manage so and in seven slides we described a per type opt in for lifetime semantics you can have a non owning handle you can have a retained handle and shared handle or a unique handle and that's just with concepts implementing that without concepts absolutely a nightmare and there's a whole bunch of side effects that I don't want to get into but I think that's a very powerful part of C++ here we can also extend this by implementing other pointer like types so hazard pointer which is meant more for concurrency related stuff boost offset pointer which is a an optimisation for shared memory operations and even if you wanted to have some weird pointer and to like go and you were binding code with C go you would be able to use this as well the execution context boundary is basically this idea of executing code at compile time versus runtime I believe oli was discussing this in their talk I missed that talk because I was trying to finish up a few slides I apologize for that but cautionary sources concise spirit constant eval is basically where we're getting into this supercilious has explored this a lot more areas our compilers are trying to implement bytecode interpreters for context per just for speed purposes so in super suppose 20 we're getting cost eval cost in it and we still have cost expert we're not going to talk about constant it it is a terrible keyword with one specific use a lot of people don't understand its meaning I am one of those people so I can't explain it even if I wanted to functions our runtime by default as they are in rust cons eval means it can only execute at compile time and in a compile time context so if you try to you know return a function from main the function will still execute a compile time but then the value that is returned will be stored and then returned in a runtime context cost expert is sometimes at compile time and this is where the bridge concept of a bridge between these two boundaries for execution context comes in we can now detect and see what suppose 20 if we are running underneath a context pert context or not and then change our code dependent on that then sequel suppose 20 we will be able to have cost expert Cindy semantics because at cons you know at compile time we just do what it would normally do in a non efficient way and at compile time we can actually insert assembly instructions right I think that that's extremely powerful and allows you to also check to see like okay because a context where function cannot invoke undefined behavior you can kind of check your stuff with static assert at compile time and allow the you know the the type system to kick into place we also support virtual cost expert which yes this is terrifying because if you think about it means that you can have a virtual cost expert destructor so we can have compiled time polymorphism in the 1990s style way of inheritance and virtual functions public inheritance and yes this also supports virtual based classes so if you remember that massive slide that everyone just like gasped in horror at the closing keynote last year that had a million virtual base classes that could technically be done at compile time as well that said though if we can do any of this I think rust can do it too I again not that part specifically I should note but just the ability to have like a dime trait B compile time I think is something that could potentially be in rust future wouldn't obviously be a Dyne trait I'd probably be a constant dine trait but that is something I think is definitely possible maybe not right now I'm not gonna write the proposal I have too many things going on in my life right now I have seventeen papers you need to get through the C++ standard so we're gonna talk about something here we're gonna be switching gears right the technical part of this talk is over with and this is we're gonna be leaning into this very slowly it's just let it build up but I promise what we over with it soon so in Ben arises talked he mentions that the FreeBSD community was telling those unhappy with system D to come to FreeBSD right and this is a problem because system DS creator even if he is an abrasive person even if you don't like him I don't think he deserves death threats and if these are the same people that are then going into the freebsd community that is a problem and those are not the people you want in a community right you don't want to find out that oh this speaker at a conference sent a death threat to someone that maintains a C++ compiler and also now they're running rust kind of like this sort of thing that happened here saying that the people in charge of C++ are idiots and that it is academic masturbation is not going to win any points with anyone and furthermore saying oh we should try to get game developers to come to rust as one gonna make everyone here have an aneurysm when you have to see all the unsafe code they're gonna write because they're gonna use the unsafe keyword trust me I've already seen some of the code that's out there and also you don't want this kind of person to be talking to people in general right like do you do you want to have a conversation with this is like oh this is a tweet from a dude that has written a book on physics in C++ and using it over the network and and he lost his absolute mind at me I also wanted to show a few tweets from the VP of Technology activision but he blocked me on Twitter when I said the game companies that make billions of dollars should maybe pay their employees a valid salary and maybe they could just send representatives to C++ if they're that upset about it so you know I and also I don't I don't think you want people like this in your milieu right in your general social environment and if we start to see other implementations arise you may not have a choice but to interact with them right just because the rust community right now has a code of conduct and just because the rust subreddit has a code of conduct does not mean that an alternative implementation of rust has to follow those same code of conduct rules and that kind of brings this into the concept of standard versus specifications so all standards are a specification but not all specifications are a standard especially if they only apply to single product right if there was a specification for the rust compiler that would just be a specification for what the rust compiler can and cannot do it does not imply that if I write my own rust compiler that I have to implement every part of said specification thus there could be a standard rust in the future where bar or CK is not a part of that right and that's one of those powerful parts of the rust compiler but it is not part of the language the borrowed checker is just a static analysis tool it is not baked into the language itself and yeah that's terrified but we're gonna put that aside for now okay we're not gonna actually bring this up again so in C++ were limited to the rules of ISO ISO actually has this hard rule of five years is them is the minimum at had time or the maximum amount of time you are allowed to release a standard between so the fact that we're doing that every three years in C++ we're kind of breaking the rules and rust is limited to the laws of the United States under which Mozilla operates right if they say you cannot provide software to someone in Iran right then all of Iran cannot use rust I could technically hand a USB Drive to someone from Germany and then that person could hand it to someone from Iran but I can't know about that at all this is where things start to get like really hairy in general ISO draws its authority from multiple nations each backed by treaties international trademark laws in some case they use their military to enforce these laws and by only the content found of this document so C++ the the working group 21 C++ Standards Committee we don't own the C++ standard the ISO you know organization owns it ISO organization ATM machine so it's so there's this concept of a standard plate of spaghetti right a plate of spaghetti against which you could technically judge all other you know plates of spaghetti and if something doesn't meet that standard plate of spaghetti it can be deemed subpar so there is in fact a minimum amount of you know cooked spaghetti that you can meet and ISO owns the copyright and Trademark for set document membership access to I so by the way changes per country in the United States it's twenty two hundred dollars a year and you can also get some of that money just made to disappear or that requirement to disappear if you make less than three million dollars as a result United States national body for ISO is massive we have tons of companies that are not based in the United States because it's just easier to join the u.s. one than it is to join their own countries ECMA is an alternative organization to ISO and draws its authority from the same sources except it's based out of Switzerland what corporations have as much of a say there's a national body if Google pay $17,000 and I n CITS the American standards body pay $17,000 they have an equal say it's also prohibitively expensive I think the the minimum amount of money you need to pay per year for voting rights is 17,000 Swiss marks or whatever their currency as I don't care anymore I don't pay attention to that stuff so Mozilla draws its authority for me it's corporate laws such as intellectual property laws that can be used to threaten permanent destitution to anyone violating them if a court scene Dean's and someone has violated these laws right if a judge says yes you are in violation of this intellectual property and as a result I'm going to find you $500 a day until you decide to come in line with these rules that can seriously limit your future and currently Chelsea Manning is I believe paying $1,000 a day for refusing to testify in front of a grand jury she could use some help financially by the way and in the above cases a person does not have the power to say something right without some labor derived a reason right so if something isn't for work then changes people's supposed to write rest might be dismissed right if I'm not doing it for a project then you can just ignore my changes this takes power away from users and replaces it with submission to Authority also I'm sorry I'm getting the note that I need to speed up here and basically wrap up so I'm just gonna skip ahead here and the the thing I'm trying to get at here I guess is that can get to a lot of this stuff I tried so hard got so far to the end didn't even matter so I guess the thing I'm trying to say is that I don't want rust to standardize I think that trying to force it into an organization that has to be backed by a nation state to enforce it is a mistake and what rust really needs is some kind of informal body to well also by the way I'm an Turkish I don't have all the answers and apparently neither do I have the time to finish this upset where's going yeah so so if in a formal body for homeless Tanner does not exist I don't know if it could exist and how you would even force any of these things it's very difficult to talk about this stuff and this is something that I would rather have had a lot more time to get to this point maybe I should have pushed it further up in the talk and you know you offer responsible yourselves new communities well since the industries we're working and I guess what's gonna closes this talk up with this you know if if you want to hide horrors and fight for major catastrophe you have to feel pain to be alone that's not language evangelism that's language Evangelion ISM and I'm sorry that this talk ended up going over the time here I guess we're out of time yeah so I will be putting these slides up on github so feel free to check that out later and if you want to actually have the important part of the talk that I wanted to get to which is please don't make a standard that has to close off access to the current milieu that is in this room that is if this conference that is at other conferences and requires people to pay to to vote I highly suggest that you you look into alternatives even if they don't exist yet even if you have to make something new [Applause] [Music] you

Channel: Rust

Views: 23,357

Rating: 4.652174 out of 5

Keywords: rust-lang, rust, rustlang

Id: YZomx3Jt4Xs

Length: 32min 21sec (1941 seconds)

Published: Mon Sep 16 2019