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Comment by RustyConsul | Hacker News Reader

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RustyConsul·

I think what he's saying is there is a way to carelessly use smart pointers in rust.

pub enum List { Empty, Elem(i32, Box<List>), }

instead of :

pub struct List { head: Link, }

enum Link { Empty, Some(Box<Node>), }

struct Node { elem: i32, next: Link, }

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Can you explain the difference between these approaches? Is it just that the first example allocates an extra u16 (tag of the tagged union) (ignoring any overhead)?

Notice that if I make this alleged "List" with a single data item in it, my data lives in the List object I just made (probably on the stack), but an empty List gets allocated on the heap.

I thought Aria's "Entirely Too Many Lists" tutorial actually tries to build this, but it actually doesn't, she draws you the resulting "list" and then is like, OK, that's clearly not what we want, let's build an actual (bad, slow, wasteful) linked list as our first attempt.

I don’t really get your example, or how does it have to do anything with rust? It’s just a bad linked list, isn’t it?

Are you talking about the example by RustyConsul? Because I'm not RustyConsul so I can't tell you what specifically RustyConsul intended with this example. Yes this is a bad data structure in Rust, or C, or presumably Zig. In the context of this thread I'm sure Zig's proponents will say that you'd never make this mistake in Zig.

My original point was referencing the use of smart pointers. They are indeed very smart, but can be used stupidly as a bandaid kind of like .clone().

The difference really lies in the fact that i now have some data stored on the stack (The element) and some data stored on the heap because it's recursive. Was just a random example of where it's poor practice. As others have noted, linkedlists are a terrible data structure to begin with.

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