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Can you show me an example of Rust promising "if it compiles it works"? This seems like an unrealistic thing to believe, and I've never heard anybody working on

Can you show me an example of Rust promising "if it compiles it works"? This seems like an unrealistic thing to believe, and I've never heard anybody working on or in Rust claim that this is something you can just provide with absolute confidence. The cost-benefit argument for Rust has always been mediated by the fact that Rust will need to interact with (or include) unsafe code in some domains. Per above, that's an explicit goal of Rust: to provide sound abstractions over unsound primitives that can be used soundly by construction.

fwip 11mo ago
I've seen (and said) "if it compiles it works," but only when preceded by softening statements like "In my experience," or "most of the time." Because it really does feel like most of the time, the first time your program compiles, it works exactly the way you meant it to. I can't imagine anybody seriously making that claim as a property of the language. (edit: fixed a comma and a forgotten word)
- woodruffw 11mo ago
  Yeah, I think the experiential claim is reasonable. It's certainly my experience that Rust code that compiles is more confidence-inspiring than Python code that syntax-checks!
treyd 11mo ago
> Can you show me an example of Rust promising "if it compiles it works"? [...] and I've never heard anybody working on or in Rust claim that this is something you can just provide with absolute confidence. I have heard it and I've stated it before. It's never stated in absolute confidence. As I said in another thread, if it was actually true, then Rust wouldn't need an integrated unit testing framework. It's referring to the experience that Rust learners have, especially when writing relatively simple code, that's it tends to be hard to misuse libraries in a way that looks correct and compiles but actually fails at runtime. Rust cannot actually provide this guarantee, it's impossible in any language. However there are a lot of common simple tasks (where there's not much complex internal logic that could be subtly incorrect) where the interfaces provided by libraries they're depending on are designed to leverage the type system such that it's difficult to accidentally misuse them. Like something like not initializing a HTTP client properly. The interfaces make it impossible to obtain an improperly initialized client instance. This is an especially distinct feeling if you're used to dynamic languages where you often have no assurances at all that you didn't typo a field name.
kstrauser 11mo ago
I've also said it, with the implication that the only remaining bugs are likely to be ones in my own logic. Like, suppose I'm writing a budget app and haven't gone to the lengths of making Debit and Credit their own types. I can still accidentally subtract a debit from a balance instead of adding to it. But unless I've gone out of my way to work around Rust's protections, e.g. with unsafe, I know that parts of my code aren't randomly mutating immutables, or opening up subtle use-after-free situations, etc. Now I can spend all my time concentrating on the program's logic instead of tracking those other thousands of gotchas.
qcnguy 11mo ago
https://hn.algolia.com/?dateRange=all&page=0&prefix=false&query=%22if%20it%20compiles%20it%20works%22&sort=byDate&type=comment https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu... Examples: 6 days ago: Their experience with Rust was positive for all the commonly cited reasons - if it compiles it works 8 days ago: I have to debug Rust code waaaay less than C, for two reasons: (2) Stronger type system - you get an "if it compiles it works" kind of experience 4 months ago: I've been writing Rust code for a while and generally if it compiles, it works. 5 months ago: If it’s Rust, I can just do stuff and I’ve never broken anything. Unit tests of business logic are all the QA I need. Other than that, if it compiles it works. 9 months ago: But even on a basic level Rust has that "if it compiles it works" experience which Go definitely doesn't. Some people claim that the quote is hyperbolic because it only covers memory errors. But this bug is a memory error, so ...
- aw1621107 11mo ago
  > Examples: GP isn't asking for examples of just anyone making that statement. They're asking for examples of Rust making that promise. Something from the docs or the like. > Some people claim that the quote is hyperbolic because it only covers memory errors. But this bug is a memory error, so ... It's a memory error involving unsafe code, so it would be out of scope for whatever promises Rust may or may not have made anyways.
  - qcnguy 10mo ago
    Rust can't make a promise, only people can. I think it was clear what samdoesnothing meant.
    - aw1621107 10mo ago
      I think it's pretty reasonable to interpret "Language X promises Y" as tantamount to said promise appearing in Language X's definition and/or docs. Claims from devs in their official capacities are likely to count as well. On the other hand, what effectively random third parties say doesn't matter all that much IMO when it comes to these things because what they think a language promises has little to no bearing on what the language actually promises. If I find a bunch of randos claiming Rust promises to give me a unicorn for my birthday it seems rather nonsensical to turn around and criticize Rust for not actually giving me a unicorn in my birthday.

fwip 11mo ago

I've seen (and said) "if it compiles it works," but only when preceded by softening statements like "In my experience," or "most of the time." Because it really does feel like most of the time, the first time your program compiles, it works exactly the way you meant it to. I can't imagine anybody seriously making that claim as a property of the language. (edit: fixed a comma and a forgotten word)

woodruffw 11mo ago
Yeah, I think the experiential claim is reasonable. It's certainly my experience that Rust code that compiles is more confidence-inspiring than Python code that syntax-checks!

treyd 11mo ago

> Can you show me an example of Rust promising "if it compiles it works"? [...] and I've never heard anybody working on or in Rust claim that this is something you can just provide with absolute confidence. I have heard it and I've stated it before. It's never stated in absolute confidence. As I said in another thread, if it was actually true, then Rust wouldn't need an integrated unit testing framework. It's referring to the experience that Rust learners have, especially when writing relatively simple code, that's it tends to be hard to misuse libraries in a way that looks correct and compiles but actually fails at runtime. Rust cannot actually provide this guarantee, it's impossible in any language. However there are a lot of common simple tasks (where there's not much complex internal logic that could be subtly incorrect) where the interfaces provided by libraries they're depending on are designed to leverage the type system such that it's difficult to accidentally misuse them. Like something like not initializing a HTTP client properly. The interfaces make it impossible to obtain an improperly initialized client instance. This is an especially distinct feeling if you're used to dynamic languages where you often have no assurances at all that you didn't typo a field name.

kstrauser 11mo ago

I've also said it, with the implication that the only remaining bugs are likely to be ones in my own logic. Like, suppose I'm writing a budget app and haven't gone to the lengths of making Debit and Credit their own types. I can still accidentally subtract a debit from a balance instead of adding to it. But unless I've gone out of my way to work around Rust's protections, e.g. with unsafe, I know that parts of my code aren't randomly mutating immutables, or opening up subtle use-after-free situations, etc. Now I can spend all my time concentrating on the program's logic instead of tracking those other thousands of gotchas.

qcnguy 11mo ago

https://hn.algolia.com/?dateRange=all&page=0&prefix=false&query=%22if%20it%20compiles%20it%20works%22&sort=byDate&type=comment https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu... Examples: 6 days ago: Their experience with Rust was positive for all the commonly cited reasons - if it compiles it works 8 days ago: I have to debug Rust code waaaay less than C, for two reasons: (2) Stronger type system - you get an "if it compiles it works" kind of experience 4 months ago: I've been writing Rust code for a while and generally if it compiles, it works. 5 months ago: If it’s Rust, I can just do stuff and I’ve never broken anything. Unit tests of business logic are all the QA I need. Other than that, if it compiles it works. 9 months ago: But even on a basic level Rust has that "if it compiles it works" experience which Go definitely doesn't. Some people claim that the quote is hyperbolic because it only covers memory errors. But this bug is a memory error, so ...

aw1621107 11mo ago
> Examples: GP isn't asking for examples of just anyone making that statement. They're asking for examples of Rust making that promise. Something from the docs or the like. > Some people claim that the quote is hyperbolic because it only covers memory errors. But this bug is a memory error, so ... It's a memory error involving unsafe code, so it would be out of scope for whatever promises Rust may or may not have made anyways.
- qcnguy 10mo ago
  Rust can't make a promise, only people can. I think it was clear what samdoesnothing meant.
  - aw1621107 10mo ago
    I think it's pretty reasonable to interpret "Language X promises Y" as tantamount to said promise appearing in Language X's definition and/or docs. Claims from devs in their official capacities are likely to count as well. On the other hand, what effectively random third parties say doesn't matter all that much IMO when it comes to these things because what they think a language promises has little to no bearing on what the language actually promises. If I find a bunch of randos claiming Rust promises to give me a unicorn for my birthday it seems rather nonsensical to turn around and criticize Rust for not actually giving me a unicorn in my birthday.