• 0 Posts
  • 110 Comments
Joined 1 year ago
Cake day: July 31st, 2023
  • pivot_root@lemmy.worldtoLinux@lemmy.ml•One Of The Rust Linux Kernel Maintainers Steps Down - Cites "Nontechnical Nonsense"
    2·
    3 months ago

    That’s not the point, though. The point is to use a nominal type that asserts an invariant and make it impossible to create an instance of said type which violates the invariant.

    Both validation functions and refinement types put the onus on the caller to ensure they’re not passing invalid data around, but only refinement types can guarantee it. Humans are fallible, and it’s easy to accidentally forget to put a check_if_valid() function somewhere or assume that some function earlier in the call stack did it for you.

    With smart constructors and refinement types, the developer literally can’t pass an unvalidated type downstream by accident.

  • pivot_root@lemmy.worldtoLinux@lemmy.ml•One Of The Rust Linux Kernel Maintainers Steps Down - Cites "Nontechnical Nonsense"
    1·
    3 months ago

    You’re going to need to cite that.

    I’m not familiar with C23 or many of the compiler-specific extensions, but in all the previous versions I worked with, there is no type visibility other than “fully exposed” or opaque and dangerous (void*).

    You could try wrapping your Foo in

    typedef struct {
    Foo validated
} ValidFoo;

    But nothing stops someone from being an idiot about it and constructing it by hand:

    ValidFoo trustMeBro;
trustMeBro.validated = someFoo;
otherFunction(trustMeBro);

    Or even just casting it.

    Foo* someFoo;
otherFunction((ValidFoo*) someFoo);
  • pivot_root@lemmy.worldtoLinux@lemmy.ml•One Of The Rust Linux Kernel Maintainers Steps Down - Cites "Nontechnical Nonsense"
    3·
    3 months ago

    If it were poorly designed and used exceptions, yes. The correct way to design smart constructors is to not actually use a constructor directly but instead use a static method that forces the caller to handle both cases (or explicitly ignore the failure case). The static method would have a return type that either indicates “success and here’s the refined type” or “error and this is why.”

    In Rust terminology, that would be a Result<T, Error>.

    For Go, it would be (*RefinedType, error) (where dereferencing the first value without checking it would be at your own peril).

    C++ would look similar to Rust, but it doesn’t come as part of the standard library last I checked.

    C doesn’t have the language-level features to be able to do this. You can’t make a refined type that’s accessible as a type while also making it impossible to construct arbitrarily.

  • pivot_root@lemmy.worldtoLinux@lemmy.ml•One Of The Rust Linux Kernel Maintainers Steps Down - Cites "Nontechnical Nonsense"
    91·
    3 months ago

    Unless you’re a functional programming purist or coming from a systems programming background, it takes a lot longer than a few days to get used to the borrow checker. If you’re coming as someone who most often uses garbage-collected languages, it’s even worse.

    The problem isn’t so much understanding what the compiler is bitching about, as it is understanding why the paradigm you used isn’t safe and learning how to structure your code differently. That part takes the longest and only really starts to become easier when you learn to stop fighting the language.

  • pivot_root@lemmy.worldtoLinux@lemmy.ml•One Of The Rust Linux Kernel Maintainers Steps Down - Cites "Nontechnical Nonsense"
    141·
    3 months ago

    The first directory block is a hole. But type == DIRENT, so no error is reported. After that, we get a directory block without ‘.’ and ‘…’ but with a valid dentry. This may cause some code that relies on dot or dotdot (such as make_indexed_dir()) to crash

    The problem isn’t that the block is a hole. It’s that the downstream function expects the directory block to contain . and .., and it gets given one without because of incorrect error handling.

    You can encode the invariant of “has dot and dot dot” using a refinement type and smart constructor. The refined type would be a directory block with a guarantee it meets that invariant, and an instance of it could only be created through a function that validates the invariant. If the invariant is met, you get the refined type. If it isn’t, you only get an error.

    This doesn’t work in C, but in languages with stricter type systems, refinement types are a huge advantage.