I was part of the team in Amsterdam on this. Insane days. Had some great engineers we hired in AMS. We were moving the whole source code into a monorepo as well which was another crazy project. I think if we had not had some of the engineers we did at those exact times, we would have not gotten out of it.
Problem here with Swift came down to
- Apple not dogfooding its own tech . Hell they did not even help us or other major companies like AirBnB and LihnkedIn (We formed a workforce on this problem with them which then forced the download limit to be upped by apple)
- Engineers deciding to adopt a language which they thought was great (and turned out not to be at the time) because they did not do the right analysis upfront for such a significant project. 'Wow look at this shiny new cool tool, lets use it' (Oversimpiification, swift was more pleasant to write with and you could be more productive which was no doubt a factor here)
Also, while management at the time didnt care for the remote offices much, I think the AMS team played a critical role in the success here. With the recent layoffs that occurred, I heard that they were fired.
Another fun story, we were trying to bring down our build times on our CI builds which were 1hr+ while battling macstadium and their crappy infrastructure with tens/hundreds of patches incoming each day.
I was an iOS engineer at Airbnb when we were battling binary size increases caused by Swift. I rewrote the watch app twice; once to migrate to watchOS 2 and once to convert it all to ObjC (which saved ~9mb). While Swift does have its problems (and had a lot more back when we worked on this), there are many factors to why the Uber app (and Airbnb) is getting so large.
Airbnb is 75% executables, 9.5% assets and 8% localizations. This is pretty different from Uber which is 60.7% executables, 26% localizations and only 3.8% assets. While the Uber executables are large, ~10mb more than Airbnb (note: this is only the Uber rider app, while Airbnb has host+guest in one app), their localizations seem to be driving a lot of the app’s 300+mb install size.
Looking at how the localizations are laid out in the app bundle, there are thousands of *.strings files in separate bundles, seems to be one for each feature. Many of these files have comments to provide context for the strings. An example from the app is: "Various screens show this as a title in a snackbar message when there is no network connectivity available". Just stripping these comments out of the localization files would save about 17.6mb of the install size. Another side effect of splitting localizations into so many files is there are over 23k duplicated strings throughout these bundles.
While the Swift code size is part of the problem with Uber’s app size, it's not the only way to free up space. There's a lot of work that goes into bringing a large scale iOS app’s size down, and not many tools to help. I left my job at Airbnb recently to work on making it easier to visualize, monitor and reduce app size, please email me (noah [at] emergetools.com) if you might be interested!
Looking at the bundle now is not going to give you insight into the problems in the Uber app 4 years ago. Also you’re looking at the uncompressed install size, which was not the problem (over the air compressed download size was the limiting factor). Strings files are extremely compressible, encrypted binaries are not (Apple has done some work in subsequent years to make them more compressible but back then they were basically uncompressible).
Absolutely right! I left out some details to try to keep the post concise. 4 years ago at Airbnb we had the watch app problem, but now a Swift watch app wouldn’t be an issue since the latest OSs don’t require embedded Swift standard libraries. The tweet that started this thread cited the 300+mb size of Uber’s app, which looks like the current install size (not thinned), that’s why I used it as the benchmark in my explanation.
Lately Apple has been featuring size more prominently on the App Store, and it appears to be displaying the install size. This is also what users see when they look at which apps are taking up storage on their device in Settings. I think it’s important to reduce both, so users see a good number and downloads are fast/efficient. It is a very welcome change that binary encryption doesn’t negate all the gains from compression anymore. I had noticed it in the numbers but looked around for an official statement and didn’t find any, if you happen to know where this was announced I’d appreciate a link!
Yes, installed size is also an issue. And on iOS tens of thousands of small files will waste a lot of space. One may say that compared to photos and videos that's small potatoes but I disagree. Efficient use of resources, memory, bandwidth, battery, etc. matters.
Parts of the binary on the App Store are encrypted so we can only get limited information from it, but the whole app bundle is available and the rest of the files are not encrypted. We’re building a startup to help monitor, analyze and reduce app size and I was able to quickly grab these statistics from the tool we’re working on, here’s a link to a quick demo: https://www.youtube.com/watch?v=3x-hLxxUNm8
I was the person that actually managed the binary size task force and proved that it was a business problem in the first place. Not all management didn’t care about AMS :)
The Amsterdam team 100% played a critical role in solving the issue (at least until apple bumped the limit). No way we would have stayed under it without you all.
Appreciate your insight, and I'm sorry to hear about the AMS team.
The OP indicates that a rewrite was necessary regardless. Even if Swift was not yet mature, do you think it was more worthwhile than rewriting in ObjC? Given that the goal was to "sustain mobile development at Uber for the next 5 years".
Secondly, I'm not a mobile developer so I don't have much context, and I'm wondering about your outlook on iOS development as a whole. Swift obviously had major problems but has supposedly gotten much better. You mention MacStadium's issues, but Apple build servers seem to be making progress with the recent AWS EC2 Mac reveal.
Is the iOS landscape turning a corner, or do you expect a new generation of bad developer experience?
A complete rewrite of a large project is risky anyway. Doing so in a language in which literally no other project of that size exists yet strikes me as insane.
I love Swift. But I've been adopting it in bits and pieces over the years. It's not just that the language has changed significantly, you also have to get used to the idioms. E.g. my early Swift code often featured Pyramid of Doom patterns, and both language innovations and better familiarity with the idioms have helped a lot with this.
One thing I was surprised not to see was a mention of their Swift 2 to 3 migration, which was terrible in my experience working on apps that were nowhere near the complexity of Uber.
Apple should have never pushed Swift as hard as it did at the time. Between the constant API changes and issues like requiring dynamic framework linkage and copying the whole runtime into every app, it was absolutely not production ready.
It was a lot of work, but we had enough staff to make it someones job for half a year or a quarter, depending on how bad the migration is. With big codebases there are other issues that pop up with every new major Xcode release that we have to migrate, mitigate or fix. For example we are still at xcode 11 because of various bugs in xcode 12. Doing the migration was annoying, but it was not much compared to all the other issues, because the fixes were tractable.
As someone who was there, a rewrite was necessary, and with hindsight we should of done it with objective-c. The original obj-c app was built with under 10 iOS engineers in mind, and now Uber had 100s of mobile engineers work on one app in some form or another.
We didn't do a simple build scalability test until we were well into the project. If we did it would of revealed swift's build problems to us. Our swift experience is what slowed down our kotlin migration significantly. Today Uber android is still a majority Java app.
Even very recently the experience of working in swift compared to the old obj-c code base isn't as good. To this day there are debugger issues, xcode responsiveness issues and a slower build time.
Hiring on the other hand would be harder now, because it's getting hard to find people who know Objective-C and it's surface ugliness scares new people away. Swift is a decent language if you don't have to have a very large code base, so most people rightfully so don't have that much Objective-C, and if you were to work in Obj-C, you might as well go work at Facebook then.
I was not part of the initial analysis team so cannot really comment if objc was more suitable as it would require to look at objc at that time and do tests etc but I suspect we would have had a more smoother experience. Though the the code at the time was bad and indeed something needed to happen to ensure future scalability of the teams and product/code, but I think there were more sane paths we could have taken. It would have cost the company more time/money and at that time the company was battling Grab, GoJek, didi, Lyft etc so we did not have time to lose. Lots of factors to take in to consideration. No real easy answer
I havent dabbled in mobile developer platform tooling for the last few years now so I cannot comment on the iOS side, all i remember is that back then it was a shitshow :) Mobile is still playing catch up to how backend infra and tooling operates, I suspect its better but probably still got a long way to go.
We could of made it work. I think the one big benefit of the rewrite was how the architecture and nullable types basically gave us one more 9 of crash free rate, which we saw after the release with swift. With ObjC I could forsee how it would of crashed a bit more, because nullables aren't hard enforced in ObjC, but I could also see how we could of stepped around that by strong guarantees in the model & network service generation code.
The Mac CI situation has gotten much worse this year, but Swift has gotten much better. Writing a large app in Swift is still a major undertaking, but there are people doing it these days.
You can enjoy coffee without grinding your own beans.
I personally find lower level programing to be frustrating and difficult. I've built an amazing career with JavaScript and C# primarily. My hobbyist projects use C# , JS and Flutter.
I can't wrap my head around things like pointers or memory management
post-ARC, Objective-C and Swift aren't very different in terms of memory management. retain and release are handled for you, and you only need to worry about retain cycles. structs in Swift change things a bit, but not that much
With swift & obj-c your coding against the same library APIs, so in many ways it's a very similar level of programming. In many ways swift is far more complicated than Obj-C. With Obj-C iOS apps your not really writing that much C vs. the pseudo-smalltalk attachment to it.
Problem here with Swift came down to
- Apple not dogfooding its own tech . Hell they did not even help us or other major companies like AirBnB and LihnkedIn (We formed a workforce on this problem with them which then forced the download limit to be upped by apple)
- Engineers deciding to adopt a language which they thought was great (and turned out not to be at the time) because they did not do the right analysis upfront for such a significant project. 'Wow look at this shiny new cool tool, lets use it' (Oversimpiification, swift was more pleasant to write with and you could be more productive which was no doubt a factor here)
Also, while management at the time didnt care for the remote offices much, I think the AMS team played a critical role in the success here. With the recent layoffs that occurred, I heard that they were fired.
Another fun story, we were trying to bring down our build times on our CI builds which were 1hr+ while battling macstadium and their crappy infrastructure with tens/hundreds of patches incoming each day.