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Language Design: Notes on Rust

Published on 2017-07-30.

It’s an impressive language, but the user interface needs a lot of work.

Short list of unnecessary weirdnesses:

  • Generics with <>. It’s 2017 by now, we know it’s a bad idea. One of the reasons why the language suffers from abominations like the “turbofish” operator ::<>.

  • Strings don’t offer indexing, because it doesn’t make sense for UTF-8. Correct! But Strings offer slicing … WAT?

  • Misuse of [] for indexed access. Having both () and [] doing roughly the same thing, especially since [] can be used to do arbitrary things, doesn’t make sense. Pick one, use the other for generics.

  • Inconsistent naming. str and String, Path and PathBuf etc.

  • :: vs. . is kind of unnecessary.

  • Mandatory semicola, but with some exceptions in arbitrary places: struct Foo; vs. struct Foo {}

  • extern crate should just go away. The compiler should get the hint that I want to use that foo crate, after adding it to the dependencies and useing it in code.

  • Closures could be made to look much closer to functions, but somehow aren’t.

  • “associated” functions in trait impls. I’d prefer separating them from normal functions and drop the self where possible.

  • Arbitrary abbreviations all over the place. It’s 2017, your computer won’t run out of memory just because your compiler’s symbol table stores Buffer instead of Buf.

  • Can someone decide on a casing rule for types, please, instead of mixing lowercase and uppercase names? Some types being “primitive” is an incredibly poor excuse.

  • Also, having both CamelCase and methods_with_underscores?

  • Library stutter: std::option::Option, std::result::Result, std::default::Default …

  • iter(), iter_mut(), into_iter() … decide prefix or postfix style and stick with it.

  • Coercions do too many things. For instance, they are the default way to convert i32 to i64, instead of just using methods.

  • Also, converting numbers is still broken. For instance, f32 to i32 might result in either an undefined value or undefined behavior. (Forgotten which one it is.)

  • Bitcasting integers to floats is unsafe, because the bits could be a signaling NaN, causing the CPU to raise an FP exception if not disabled.

  • Forward and backward annotations: #[foo] struct Foo {} vs struct Foo { #![foo] }.

  • Type bounds are Sized by default, with some weird special syntax to opt out (?Sized).

  • /// for normal documentation, //! for module level documentation. Documentation already uses Markdown, so maybe just let people drop a markdown file in the module dir? That would make documentation much more accessible when browsing through GitHub repositories.

  • Also, documentation can cause compiler errors … that’s especially fun if you just commented a piece of code for testing/prototyping.

  • Type alias misuse: In e.g. io crate: type Result<T> = Result<T, io::Error> … just call it IoResult.

  • Macros are not very good. They are over-used due to the fact that Rust lacks varargs and abused due to the fact that they require special syntax at call-site (some_macro!()).

  • Pattern matching in macros is also weird. x binds some match to a name in “normal” pattern matching, but matches on a literal “x” in “macro pattern matching”.

  • println! and format! are very disappointing given that they use macros.

  • Compiler errors … ugh. So many things. My pet peeve: “Compilation failed due to 2 errors” … 87 compiler errors printed before that.

Overall, it’s a very impressive language with a clear vision and priorities. Also, the collection library is much better than Scala’s.