Dave Herman’s contributions to Rust

Re:Dave Herman’s contributions to Rust by da39a3ee on Wednesday May 05, 2021 @08:35PM (#27057743)

OK, that would be nice but...what you're saying just doesn't work! The user gets an error message saying

  thread 'main' panicked at 'foo invariant upheld'

And everyone, except those who are inured to the illogic via experience, will read that as

  thread 'main' panicked because 'foo invariant upheld'

especially new users, less experienced programmers, and non-Rust programmers seeing the panic message.

Now if the Rust language made that error message say

  thread 'main' panicked at failed expectation for 'foo invariant upheld'

that might be cool. But it does not do that. It feels like you're bending over backwards trying to excuse what is clearly a wart in a beautiful language. I'm happy to continue the debate though, I am fascinated to know how I can be wrong here :)

So that's my main point, that your strategy doesn't work due to the error message. But a secondary point is that Rust documentation encourages people to use it opposite to what you suggest: I mean, just look at the first example in the Rust book. It's completely nonsensical:

  let f = File::open("hello.txt").expect("Failed to open hello.txt");

I know there was some controversy about this early on and somehow it didn't get reverted; it would be more honest if the docs would at least admit that it's "a little strange".

https://doc.rust-lang.org/book/ch09-02-recoverable-errors-wi...

Playground if you want to remind yourself of the psychological experience of seeing that error message at run time with minimal effort.

https://play.rust-lang.org/?version=stable&mode=debug&editio...

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Re:Dave Herman’s contributions to Rust by iudqnolq on Thursday May 06, 2021 @05:50PM (#27069462)

Outside of tests and toy examples you're generally expected to only panic when the developer has failed to uphold an invariant, not when the user has. As a result there's generally nothing a non-rust-developer can do with the message besides post it on the bug tracker.

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Re:Dave Herman’s contributions to Rust by da39a3ee on Thursday May 06, 2021 @09:34PM (#27070949)

Right, so that's relevant to a minor incidental comment I made. But what do you think of the main points, which are

(a) If you write the message the way you suggest the printed error message is misleading, and

(b) The Rust community does not encourage using .expect() in the way you suggest; in particular the canonical Rust documentation source instructs us to use it as

  foo.expect("A thing I do not expect")

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Re:Dave Herman’s contributions to Rust by da39a3ee on Sunday May 09, 2021 @08:57AM (#27095584)

Similarly, from the rust stdlib docs for process::Command

  let hello_1 = echo_hello.output().expect("failed to execute process");

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