Shafik Yaghmour

Compiler Dev(LLDB) interested in C++, C, compilers and undefined behavior.

CppCon 2021 Trip Report

31 Oct 2021 » C++, learning

CppCon 2021 was a hybrid format this year due to Covid-19 still not being done with us. Folks were allowed on site with proof of vaccination but folks were also allowed to attend completely remote. Last year was fully online and that was a pretty positive experience for me. This year I still wasn’t sure what to expect since I was attending remotely because it was a hybrid format. The schedule was shifted earlier US time-wise to allow those in Europe to still participate live. It also meant that some content would not be broadcast the same day but the next day and as I learned later some content was only at the venue. Like last year, it was fatiguing to watch videos for long stretches of time but getting up to moving around and stretching helped.

There were a lot of changes from last year for the remote users. There were multiple interfaces to the conference for one thing. I felt like they outdid themselves this year, it felt pretty fancy and slick but also slightly overwhelming at first. One interface was a Online Platform/Web Interface through Digital Medium where you get quick access to the talks from each track, the schedule, recordings of previous talks, quick links to resources etc. I found myself mainly using this, it was quick to get to the talk you wanted to and to find previous recorded talk through that interface. There was a Virtual Venue though Gather Town which featured an accurate overhead representation of the Gaylord Rockies conference venue. You had an avatar, you could walk through the virtual conference site and goto the various talks that way as well. The Gather Town interface allowed you to enable voice and video, if you were next to other virtual participants you could see and hear them if they had their voice or video on. The other piece of the conference was a CppCon Discord server. The conference used this to communicate updates, makes announcements and a help-desk was also available. You could also use Discord to socialize with conference participants on various channels.

The virtual venue felt like playing an overhead role playing game. They added a set of puzzles that could be found around the virtual venue if you looked hard enough. Solving each puzzle earned you points and you could check your progress on a leader board in the virtual environment. The puzzles mainly consisted of C++ trivia of varying degrees of difficultly. Several of the puzzles were more difficult pieces of C++ history. I learned something I did not know about before that in 1994 Erwin Unruh created a template meta program that calculated the prime numbers in error messages showing that templates are Turing complete. You can still find the original version but it does not work on modern compilers.

I found the mixed interfaces to be stumbling block, it took half a day to really figure out what worked for me and how to find what I wanted. They provided a pretty detailed document with nicely marked up pictures but it was a lot to absorb, it didn’t really click until you actually had to use it. During the weekend before, I found the virtual venue fun and solved a lot of puzzles but once the talks started I found that being able to quickly get to a talk more important and dropped the virtual venue. That also meant that I did not socialize at all during the event. I am not sure how I would have changed things. I think each individual interface worked very well but once I started out using the web interface it was hard to go back to the virtual one. Part of that was the reality of still being in my day to day world which has its own demands while attending the conference remotely.

What about the talks? Last year I did the five must see talks. This year I want to highlight the five talks I felt either:

  • Presented a complicated subject in clear and concise way
  • Gave us a vision for C++ in an inspiring way
  • Helped us to understand what on the outset does not seem like a deep or widely applicable problem and showed how, yes, you should care about this and how it applies more widely.

I also picked one of the lighting talk sessions. I will link to each speakers twitter account if it exists as well as the talk once it becomes available online. Here are my picks for talks to watch from the CppCon 2021:

  • Embracing User defined literals for safely for types that behave as though builtins

    By @PabloGHalpern

    This talk not only explained the mysterious subject of user defined literals but also delved into the safety aspects around this language feature. This was the first good explanation I have seen of this feature. I did not realize how rich a feature this was and the problems that it allows one to solve. There are also plenty of pitfalls that you have to watch out for but after watching this talk I think you will be in a good place to use them wisely.

  • C++20 Templates: The next level: Concepts and more

    By @Andreas__Fertig

    I have to say, this was my favorite talk, it was a well polished talk. I have spent some time looking at concepts but never really in depth, I guess because I am not
    writing library like code most of the time. I came away with a much better understanding of concepts and the rationale for a lot of tricky pieces such as requires requires and compound requirements. He managed to fit a lot of information in each slide in a way that did not feel overwhelming. I know I will be able to go back to the slides and they will be a great references.

  • Lighting talks with Michael Caisse

    Lighting talks are hit or miss but the first set of lighting talks hosted by Michael Caisse were pretty much all solid and well worth watching, each talk although short felt liked it was packed solid content. From Walter Brown’s talking about “Loop Unrolling” to @ben_deane talking about “The Process is the Problem”. They each landed well in the short time they had. Don’t miss these lighting talks.

  • Extending and Simplifying C++: Thoughts on pattern Matching using is and as

    By @herbsutter and @seanbax

    Herb’s talk was a visionary talk about how to make C++ more expressive using operator is and operator as. He explained how we can use these operators to replace a whole set of type query and type cast operations. He also demonstrated how they could also be applied to standard library types such as std::variant and std::optional. He was joined on stage for a set of three demos by Sean who has implemented these features in his Circle C++ Compiler. I felt like the talk made an solid argument for how these features could transform the language to make it more expressive and safer. They provided godbolt links on the slides so folks can try this out for themselves. Hopefully folks will take the opportunity to write some code using this feature and help drive constructive feedback on the proposal.

  • Correctly Calculating min, max, and More: What Can Go Wrong?

    By Walter Brown

    Many in the C++ community have known that std::min and std::max have design issues. So at first I was like, “I know what this is about, maybe I should skip it”. I am happy I did not listen to that part of me. He took a wider perspective and explained what the issue was and why this is not specific to std::min or std::max but is a wider more applicable issue. He explained why this is related to operator < and introduced a out_of_order and and in_order and why looking at the various problem through a different lens allows us to avoid algorithmic pitfalls. He walks through the many different “spellings” or operator < and various implementations of each one. There is a lot of food for thought packed into a relatively short time. You will be thinking about this talk longer afterwards.

  • What You Can Learn from Being Too Cute: Why You Should Write Code That You Should Never Write

    By @Daisy Hollman

    I loved the energy of this talk, she spent time to learn some really interesting dark corners of C++ and figured out how to do interesting and cursed things with them. All the while having fun and I would say learning is always profit. Then she distills the essence of each piece and walks us step by step through it so that we can understand why it works, what part of the language explains this and the caveats around it. Learning about dark corners of C++ can be rewarding but figuring out how to communicate that to broader community is way more rewarding and also gives back and helps others learn. Some will know this to be an area dear to me as I often plumb the dark corners of C++ writing my Weekly C++ quizzes on twitter. I also often post cursed code on twitter but usually leave it as an exercise to the user to figure out what is going on. Maybe this will inspire me to do some more detailed posts in the future 🤔

I learned a lot during this conference and the only downside was that Walter Brown’s “Computing in the 1960’s” talk was Open Content talk and it won’t be posted online. The past few years I have grown more interested in the history of how we got to where we are with C++ and programming languages in general. A few years ago I spent time rereading “Design and Evolution of C++. It gave me perspective on how a programming language evolves and can make dramatic improvement over time with thought and carefully balancing of trade-offs. I am sure Walter’s talk was full of perspective and hopefully he will give it again.