• Ephera@lemmy.mlEnglish
    39·
    2 months ago

    The rule of thumb I always tell people is that they should generally put owned data into struct fields and references into function parameters.

    • calcopiritus@lemmy.world
      17·
      2 months ago

      Good rule of thumb. As long as it’s not followed blindly of course.

      Structs with lifetimes are often quite convenient. Especially for performance.

      • Ephera@lemmy.mlEnglish
        1·
        2 months ago

        Ah yeah, via deref coercion, which is also called “auto-dereferencing” at times. Not to be confused with “auto-referencing”, which is also a thing[1].

        You can do some wild shit with deref coercion. And when I say “wild”, I guess, I’m talking about the most normal thing for Java devs, because well, it’s a lot like inheritance. 😅

        Basically, this concept of being able to pass &String into a parameter that takes &str also applies to the self parameter. Or in other words, methods implemented on str can also be called on String, as if String extends str.
        And well, obviously you can also make use of that yourself, by writing your own wrapper type. You can even “override” existing methods in a sense by re-defining them in the wrapper type.

        I had to play around a bit with it myself, so here’s a playground: https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=af65ed396dec88c8406163acaa1f8f8d

        1. https://doc.rust-lang.org/nomicon/dot-operator.html ↩︎

  • marcos@lemmy.world
    32·
    2 months ago

    That’s how the C++ code should have looked all the time. And the amount of people that get surprised and complain about this is just more evidence that nobody should write C++. Ever.

      • Ephera@lemmy.mlEnglish
        12·
        2 months ago

        I guess, if you come from garbage-collected languages, you might be used to not needing the ampersands, because everything is automatically a reference in those…

        • XPost3000@lemmy.ml
          6·
          2 months ago

          Yeah this is how it was for me when I first started C++, I was use to any object beyond a simple 3D vector to always be passed by reference

          And then I read a C++ book my uncle gave me during a flight and realized that there isn’t any syntax for passing a parameter by copy, so obviously that’d have to be the default behavior and I’ve been passing by reference ever since

          • Ephera@lemmy.mlEnglish
            7·
            2 months ago

            Oh wow, what the hell. I’m not actually familiar with C++ (just with Rust which gets similar reactions with the ampersands), but that’s insane that it just copies shit by default. I guess, it comes from a time when people mostly passed primitive data types around the place. But yeah, you won’t even notice that you’re copying everything, if it just does it automatically.

            And by the way, Rust did come up with a third meaning for passing non-references: It transfers the ownership of the object, meaning no copy is made and instead, the object is not anymore allowed to be used in the scope that passed it on.
            That’s true, except for data types which implement the Copy trait/interface, which is implemented mostly for primitive data types, which do then get treated like C++ apparently treats everything.

            • KmlSlmk64@lemmy.world
              4·
              2 months ago

              There are also the move semantics in C++, which are similar to Rust’s ownership transfer, but explicit and with some differences in how the data is actually handled under the hood