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452 points birdculture | 1 comments | | HN request time: 0.333s | source
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Animats ◴[] 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...

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psychoslave ◴[] 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?

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Renaud ◴[] No.43981185[source]
I find it strange that you relate borrowing and ownership to financial asset management.

From that angle, it indeed doesn’t seem to make sense.

I think, but might be completely wrong, that viewing these actions from their usual meaning is more helpful: you own a toy, it’s yours to do as tou please. You borrow a toy, it’s not yours, you can’t do whatever you want with it, so you can’t hold on to it if the owner doesn’t allow it, and you can’t modify it for the same reasons.

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1. ithkuil ◴[] No.43981643[source]
Analogies often leak.

1. In real life I can borrow a toy from you and while I have that toy in my hands, the owner can exchange ownership with somebody else, while the object is borrowed by me. I.e. in real life the borrowing is orthogonal to ownership. In rust you can't do that.

2. Borrowing a toy is more akin to how mutable references work in rust. Immutable references allow multiple people to play with the same toy simultaneously, provided they don't change it.

Analogies are just analogies