One of the things I like to do is compare how different languages solve the same problem — especially when they end up having very different approaches. It’s always educational. In this case, a bunch of us have been working hard on trying to get reflection — a really transformative language feature — into C++26. Fundamentally, reflection itself can be divided into two pieces:

This is a blog post that really is about C++, but with a look at how Rust does things. So, this is an interesting C++/Rust comparison for once.

  • @BB_C
    1•2 hours ago

    In Rust, you provide a string — that is injected to be invoked internally. In C++, we’d just provide a callable.

    This is because Rust’s attribute grammar can’t support a callable here.

    I don’t do C++ as a life choice, and thus not 100% sure what the author means here. But I have the feeling that he is wrong, on multiple levels even 😉

    • TehPersEnglish
      1•1 hour ago

      Correct - Rust’s attribute grammar allows any parseable sequence of tokens enclosed in #[attr ...] basically. Serde specifically requires things to be in strings, but this is not a requirement of modern Rust or modern versions of syn (if you’re comfortable writing your own parser for the meta).

      The author is not a Rust expert though, so I’m not surprised to see this assumption. It doesn’t take away from the article though.

      Edit: for fun, syn has an example parsing an attribute in an attribute

      • @BB_C
        1•59 minutes ago

        Not only that. We don’t just “inject” raw strings with the syn/quote duality. Stringified or not, the token tree will be parse-checked into the expected syn type before being used in generated code.

        So the distinction is both wrong and irrelevant. This is what I meant by wrong on multiple levels/layers 😉