←back to thread

Flattening Rust’s learning curve

(corrode.dev)
451 points birdculture | 1 comments | 13 May 25 22:25 UTC | HN request time: 0.231s | source
Show context
Animats ◴[14 May 25 00:22 UTC] No.43979394[source]▶
It's like reading "A Discipline of Programming", by Dijkstra. That morality play approach was needed back then, because nobody knew how to think about this stuff.

Most explanations of ownership in Rust are far too wordy. See [1]. The core concepts are mostly there, but hidden under all the examples.

    - Each data object in Rust has exactly one owner.
      - Ownership can be transferred in ways that preserve the one-owner rule.
      - If you need multiple ownership, the real owner has to be a reference-counted cell. 
        Those cells can be cloned (duplicated.)
      - If the owner goes away, so do the things it owns.

    - You can borrow access to a data object using a reference. 
      - There's a big distinction between owning and referencing.
      - References can be passed around and stored, but cannot outlive the object.
        (That would be a "dangling pointer" error).
      - This is strictly enforced at compile time by the borrow checker.
That explains the model. Once that's understood, all the details can be tied back to those rules.

[1] https://doc.rust-lang.org/book/ch04-01-what-is-ownership.htm...

replies(17): >>43979460 #>>43979907 #>>43980199 #>>43981064 #>>43981313 #>>43981587 #>>43981720 #>>43982074 #>>43982249 #>>43982619 #>>43982747 #>>43983156 #>>43984730 #>>43988460 #>>43990363 #>>43996196 #>>44008391 #
psychoslave ◴[14 May 25 05:15 UTC] No.43981064[source]▶
This explanation doesn't expose anything meaningful to my mind, as it doesn't define ownership and borrowing, both words being apparently rooted in an analogy with financial asset management.

I'm not acquainted with Rust, so I don't really know, but I wonder if the wording plays a role in the difficulty of concept acquisition here. Analogies are often double edged tools.

Maybe sticking to a more straight memory related vocabulary as an alternative presentation perspective might help?

replies(4): >>43981185 #>>43981730 #>>43981880 #>>43982812 #
1. arnsholt ◴[14 May 25 07:32 UTC] No.43981880[source]▶
The way I think about it is more or less in terms of how a C program would work: if you assume a heap allocated data structure, the owner is the piece of code that is responsible for freeing the allocation at the appropriate time. And a reference is just a pointer with some extra compile time metadata that lets the borrow checker prove that the reference doesn’t outlive the referent and that there’s no mutable aliasing.