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Comment by muvlon

2 days ago

C's lack of all of

- sum/union types

- multiple return values/tuple types

- exceptions

means that most ways of returning an error from a function are not available in C. Because of this, many C APIs, including `crypt` in this case, resort to in-band error signalling by using a sentinel value (like NULL, a negative integer, "*" etc.).

Most other languages lack one or two of the above, but very few lack all three, and so most have developed a different culture around error reporting (Result in Rust, multiple return values in Go, exceptions in Java, Python etc.).

21 comments

muvlon

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tialaramex  2 days ago

One of the small but important significances of Rust is that it very often gets to have the same machine code as a correct "in-band error signalling" strategy from C but with source code that the maintainers can actually understand.

And really often when your "in-band error signalling" in Rust is more expensive you realise (perhaps to your horror) that your C wouldn't be correct, so you just dodged a bullet. For example Option<OwnedFd> is, like OwnedFd, a 32-bit value, Unix has always reserved -1 to mean invalid, so Rust can treat that as a niche. But the Windows equivalent Option<OwnedHandle> can't do this because, well, cue Raymond Chen: https://devblogs.microsoft.com/oldnewthing/20040302-00/?p=40...

  • creata  2 days ago

    > One of the small but important significances of Rust is that it very often gets to have the same machine code as a correct "in-band error signalling" strategy from C but with source code that the maintainers can actually understand.

    But aside from NonZero- and NonNull-based layout optimizations, I don't think Rust is doing anything special to obtain that machine code - it's just relying on LLVM to optimize things.

    • tialaramex  1 day ago

      Well, all of the niche optimisations, so that includes every normal C-style user-defined enumeration because (unlike C or C++) Rust says those aren't just the integers wearing a funny hat.

      But sure, for the most part LLVM will do The Right Thing™ here without much help and Rust is just giving better ergonomics to the same backend.

Gibbon1  1 day ago

I remember mucking with returning multiple values as anonymous structs. It was tantalizing close but no banana.

I think with C23 you got half a banana now. Still can't do it because C23 didn't adopt proposals to allow returns of untagged/anonymous structs.

If you could then you could write

  auto rtn = Foo();
  if(rtn.err) 
    printf("err=%i", rtn.err);
  else
    printf("Foo=%i\n", rtn.foo);

jppittma  2 days ago

C has sum types/unions? What are you talking about? You don't need multiple return. You can use a struct and it's the same thing.

  • adgjlsfhk1  2 days ago

    not in a way that forces the user to actually handle them properly. C is a weakly typed language and as such is pretty badly suited to systems programming.

    • uecker  2 days ago

      C is not a weakly typed language, this is just nonsense. There is also [[nodiscard]] which you can use to make sure a return value is handled.

      4 replies →

  • muvlon  2 days ago

    C unions are sum types if you just "draw the rest of the fucking owl". C has sum types the way x86 assembly has function calls. You see, there are "call" and "ret" instructions. Just figure out calling convention and the stack yourself, it's easy. And yes I can stick the tag next to the union myself in C and write a bunch of functions that hopefully deal with it correctly. I can even write some macros that look like pattern matching and maybe convince myself that it's a language feature, but it just isn't.

    And it's very evident why the difference matters. People gravitate to what's readily available and ergonomic. That's why every C API under the sun (most definitely including libc itself) does janky stuff like returning -1 or "*" on error instead of building their own bespoke Result-style abstraction. A programming language is not just the things that are in some way possible within it, but more importantly the things that are easy in it.

    • uecker  2 days ago

      While I agree that this should come out of the box, the "rest of the fucking owl" is a tiny macro or function, so not exactly something difficult to do complex as "drawing an owl" would imply.

      4 replies →