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Comment by Jensson | Hacker News Reader

But C++ programmers have ergonomic vectors in the standard library. There is no reason to implement data structures there unless you need them for performance reasons.

And correct use of linked lists is not uncommon at all. Binary trees are linked lists for example, would you implement binary trees as a vector pointing to vectors rather than a linked list containing pointers to similar linked lists?

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Yes, I would avoid implementing my own binary tree using linked lists (unless it was just an educational exercise). But also yes, if I did decide that I had a production use case for creating my own binary tree implementation, I would be very likely to look for approaches that use contiguous rather than linked data structures.

I think this perspective you're espousing is "sometimes you just want to knock out a simple bespoke binary tree implementation", but I just don't think that use case makes sense. Either you want to use one from a good library or you have a really good reason to roll your own and it is worth the effort to do it well.

> I think this perspective you're espousing is "sometimes you just want to knock out a simple bespoke binary tree implementation", but I just don't think that use case makes sense. Either you want to use one from a good library or you have a really good reason to roll your own and it is worth the effort to do it well.

There is no library for generic tree data structures, you have to implement those yourself. There are libraries implementing a table interface using ordered binary trees but that is just one of many use cases.

Coincidentally I was just watching this talk from Bryan Cantrill: https://youtu.be/vvZA9n3e5pc. Around the 58 minute mark he shares an anecdote that is relevant to this thread. It boils down to him doing something where he would have written a simple bespoke balanced binary tree in C, but when writing a reimplementation in Rust used a "naive" library approach and was surprised to see a 35% speedup, which boiled down to the library using a btree instead of a balanced binary tree.

This doesn't invalidate your point about there being use cases for binary trees that may necessitate you to write your own, I take you at your word that you've often had strong use cases for this, but I do think it illustrates something I believe to be true, which is that people reach for linked data structures too often, when contiguous ones are a better default.

No, I probably would use the BTreeMap in std instead, assuming I want a search tree. Which is even better, because the primary reason you use binary trees in C is that they are easy to make intrusive. But if I want a priority queue instead there's also BinaryHeap. If I wanted to store data on the branch nodes I might use intrusive_collections. Or maybe if I was dealing with a more complex graph I'd pull in a library like petgraph. If all that fails I could still arena-allocate the nodes to get around the lifetime issues. If I really absolutely wanted to, which I don't see happening any time soon, personally. I'd need a more concrete example there.

I said binary tree, not "Map interface implemented using an ordered binary tree". They are not the same thing.

I am aware, as you might be able to gather by reading past the first sentence of my comment. Of course if you'd just said what you needed the binary tree for, I could have given you a better answer.

If you don't have a use case in mind, I'd suggest just trying to actually use Rust for something instead of spending time trying to construct problems where Rust would be bad at the solution.

You can't even explain how doing something as simple as a binary tree with parent pointer is possible in rust, so my assumption is that it isn't possible and I'd have to make work arounds. I can make work arounds just fine in C++, you don't have to teach me those, but I don't see why I'd learn a language where I'd be forced to make those work arounds rather than use the version that fits my problem best.

It might be possible that you can write nice versions etc, if so I'd like to see them, but it seems everyone is hell bent on just saying "You shouldn't do it!".

> You can't even explain how doing something as simple as a binary tree with parent pointer is possible in rust, so my assumption is that it isn't possible

A beginner learns this in the first week:

    struct Node<'a, 'b> {
        left: Option<&'a Node>,
        right: Option<&'b Node>
    }

Many people don't know how to read or write, but you don't hear them every day claiming that "therefore it must be impossible", yet here we are.

> but I don't see why I'd learn a language where I'd be forced to make those work arounds rather than use the version that fits my problem best.

> but it seems everyone is hell bent on just saying "You shouldn't do it!".

The claim was and still is "there are infinitely more effective - as in faster - ways to learn Rust than by starting with how to write doubly-linked lists".

This whole thread is you failing at 3rd grader logic hard and concluding:

- therefore it is impossible to write doubly-linked lists in Rust

- therefore doubly-linked list in Rust are efficient

- therefore it is impossible to learn Rust

- ...and many other things...

I've taught Rust to a 9th year old, but I don't think I could have taught Rust to a 2 year old, so arguably, I think you are right, in that probably _FOR YOU_ it is impossible to learn Rust, you wouldn't be able to grok how to write doubly-linked lists in Rust properly, you wouldn't be able to master Rust to write efficient code in it, etc.

That's ok, don't be frustrated by it, everybody is different.

Just try to stop projecting your limitations to other people. Particularly in this forum, or when talking with Linux kernel developers, were most people are smart experienced programmers that would learn Rust well in a day and master it in a week.

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