5 ms·

Sample Code: ======================= fn transmute_lifetime<'a, 'b, T>(t: &'a (T,)) -> &'b T { match (&t, ()) { ((t,), ()) => t, } } =====

Sample Code: ======================= fn transmute_lifetime<'a, 'b, T>(t: &'a (T,)) -> &'b T { match (&t, ()) { ((t,), ()) => t, } } ======================= I thought Obfuscated-C was hard to read. Then C++ with all its templates. Now, I'm thinking Rust has taken the prize.

TheDong 8y ago
If you're familiar with rust syntax, that function is readable: A function 'transmute_lifetime' that takes a tuple of generic type T with lifetime 'a and returns a T with lifetime 'b... And then the code itself, beyond the function signature, is trivial destructuring matching. If you're not familiar with the syntax of a language, of course it won't be easy to read. perl and bash can rapidly devolve into symbol salad if you don't know them. If you don't know es6, javascript's spread and destructuring assignment syntax can look every bit as strange. That all being said, the point of this rust code was to be a minimal example. Minimal reproducers are often nonsensical and unidiomatic, which helps put this in further context. I think the original un-minimized crashing code was this: https://github.com/rust-lang/rust/issues/52213#issuecomment-403894598 https://github.com/rust-lang/rust/issues/52213#issuecomment-... That's clearly more readable, and that's what more typical rust looks like.
- webaholic 8y ago
  and that is where the problem lies. All code is readable if you spend an hour or two. The point is that it is not lucid. You have to strain to understand such code. The issue is people thinking this code is acceptable.
  - TheDong 8y ago
    It's not being presented as acceptable code for maintenance or other long-term usage. It's being presented as a terse explanation of what the bug was and how it was triggered. I didn't spend an hour or two understanding that code, I spent less than a minute because I already know rust. I don't understand your point. The code served its purpose well: for the audience (rust users) it demonstrated the bug (lifetime unsafety in match ergonomics change). If the audience were "people who don't know rust", then of course that code wouldn't be a good demonstration, but that's not who the audience for this post is.
  - matthewmacleod 8y ago
    Expressing complex concepts almost always requires complex expressions of intent! I don’t really know Rust all that well beyond a few toy projects. But if you were familiar with core aspects of the syntax and semantics - lifetimes, generics, tuples and the void type in this case - then it’s not particularly complex. Add to the fact that it’s code you’re not actually going to see in practice and I don’t think it’s so bad!
  - pcwalton 8y ago
    That code is not "acceptable". It's not supposed to be. It's a compiler test case.
  - ketralnis 8y ago
    What is a language that you claim I can't find a similarly difficult sample of?
Slaul 8y ago
The post says Rust 1.27.2 will reject that code.
pcwalton 8y ago
Nobody would ever write that code in practice, for multiple reasons: - Every reference has a different explicit lifetime—one input, one output—which would rarely ever show up in real code. - There is a tuple with 1 element, which I have never seen in the wild. - It's matching against `()`, the void type, which is never done because it's useless.
ljklkjaaaammbb 8y ago
Inflammatory nonsense.
ameixaseca 8y ago
Beauty lies on the eyes of the observer. Also, there's nothing obfuscated here, and everything is explicit if you know the syntax. The alternative is not caring and leaving everything for a GC and/or validating values with runtime checks instead. There are other languages which chose these approaches.
kibwen 8y ago
This is obfuscated code designed to exploit an obscure edge case in the compiler, and then minified for concision in the test case. :P
phyzome 8y ago
It's repro code for a compiler bug, of course it looks horrible. Here's a similarly horrible Java example, from a recent HN post on Java's type system being unsound: https://twitter.com/joshbloch/status/822948565433466881 https://twitter.com/joshbloch/status/822948565433466881 It's more verbose, because Java, but equally dense relative to the language as a whole. This is not supposed to be good code.

TheDong 8y ago

If you're familiar with rust syntax, that function is readable: A function 'transmute_lifetime' that takes a tuple of generic type T with lifetime 'a and returns a T with lifetime 'b... And then the code itself, beyond the function signature, is trivial destructuring matching. If you're not familiar with the syntax of a language, of course it won't be easy to read. perl and bash can rapidly devolve into symbol salad if you don't know them. If you don't know es6, javascript's spread and destructuring assignment syntax can look every bit as strange. That all being said, the point of this rust code was to be a minimal example. Minimal reproducers are often nonsensical and unidiomatic, which helps put this in further context. I think the original un-minimized crashing code was this: https://github.com/rust-lang/rust/issues/52213#issuecomment-403894598 https://github.com/rust-lang/rust/issues/52213#issuecomment-... That's clearly more readable, and that's what more typical rust looks like.

webaholic 8y ago
and that is where the problem lies. All code is readable if you spend an hour or two. The point is that it is not lucid. You have to strain to understand such code. The issue is people thinking this code is acceptable.
- TheDong 8y ago
  It's not being presented as acceptable code for maintenance or other long-term usage. It's being presented as a terse explanation of what the bug was and how it was triggered. I didn't spend an hour or two understanding that code, I spent less than a minute because I already know rust. I don't understand your point. The code served its purpose well: for the audience (rust users) it demonstrated the bug (lifetime unsafety in match ergonomics change). If the audience were "people who don't know rust", then of course that code wouldn't be a good demonstration, but that's not who the audience for this post is.
- matthewmacleod 8y ago
  Expressing complex concepts almost always requires complex expressions of intent! I don’t really know Rust all that well beyond a few toy projects. But if you were familiar with core aspects of the syntax and semantics - lifetimes, generics, tuples and the void type in this case - then it’s not particularly complex. Add to the fact that it’s code you’re not actually going to see in practice and I don’t think it’s so bad!
- pcwalton 8y ago
  That code is not "acceptable". It's not supposed to be. It's a compiler test case.
- ketralnis 8y ago
  What is a language that you claim I can't find a similarly difficult sample of?

Slaul 8y ago

The post says Rust 1.27.2 will reject that code.

pcwalton 8y ago

Nobody would ever write that code in practice, for multiple reasons: - Every reference has a different explicit lifetime—one input, one output—which would rarely ever show up in real code. - There is a tuple with 1 element, which I have never seen in the wild. - It's matching against `()`, the void type, which is never done because it's useless.

ljklkjaaaammbb 8y ago

Inflammatory nonsense.

ameixaseca 8y ago

Beauty lies on the eyes of the observer. Also, there's nothing obfuscated here, and everything is explicit if you know the syntax. The alternative is not caring and leaving everything for a GC and/or validating values with runtime checks instead. There are other languages which chose these approaches.

kibwen 8y ago

This is obfuscated code designed to exploit an obscure edge case in the compiler, and then minified for concision in the test case. :P

phyzome 8y ago

It's repro code for a compiler bug, of course it looks horrible. Here's a similarly horrible Java example, from a recent HN post on Java's type system being unsound: https://twitter.com/joshbloch/status/822948565433466881 https://twitter.com/joshbloch/status/822948565433466881 It's more verbose, because Java, but equally dense relative to the language as a whole. This is not supposed to be good code.