‹ BackHN Continuity

Thread

C++26: Trivial infinite loops are no longer undefined behaviour

173 points · 290 comments · ibobev

  1. BobbyTables2 · · focus · HN ↗
    TLDR: For almost 1/6 of a century, the C++ standards broke the simplest infinite loop and only just recently fixed it.

    Idiots!

    Don’t they really that people write real programs to solve real problems? This isn’t a theoretical academic exercise!

    1. bryanlarsen · · focus · HN ↗
      They also realized that people choose compilers based on performance benchmarks, and that insane optimizations let them win.
      1. vlovich123 · · focus · HN ↗
        Until Rust proved actually you can get really good or better performance if the language itself is better. I really don’t know how C++ digs itself out of the UB hole it has dug.
        1. bryanlarsen · · focus · HN ↗
          Probably by working together with Rust. Eliminating undefined behavior from unsafe Rust is a big deal for the Rust community at the moment. And given that most unsafe rust code exists to call into C or C++, concepts like pointer provenance need to be extended. And proper pointer provenance guarantees can both decrease UB and increase optimization potential.

          IIUC, my understanding is shallow.

          1. nicoburns · · focus · HN ↗
            This particular case is likely an example of that. Rust used to have this problem, but it wasn't ever intended to. So IIRC it got fixed in LLVM for Rust, and this is probably now C++ taking advantage of that.
          2. vlovich123 · · focus · HN ↗
            That's a niche level thing that helps in some scenarios, and generally not as much for C++ which is much more weakly typed than Rust is. Weak typing + static typing is why safety problems in C++ are going to be really difficult to fix without fundamentally changing the language.
            1. bryanlarsen · · focus · HN ↗
              I expect some changes to the language from this direction, some way to attach provenance information or limitations to a pointer. Presumably through a #pragma at first. Strict typing in the C++ sense, not the Rust sense. An annotation like "volatile".

              Pointer provenance is just one example, there are others.

Open on Hacker News to reply ↗

Unofficial Hacker News client; not affiliated with Y Combinator.