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Comment by MereInterest | Hacker News Reader

I’m not sure. Looking through different Rust libraries, I tend to see three different styles, depending on previous programming experience. Each mimics the prior experience, with benefits.

* Everything is a struct with concrete types. This is closest to C. It benefits from the improved memory safety, without sacrificing speed.

* Everything is a Box<Rc<T>>. This is closest to dynamic garbage-collected languages, but with vastly improved performance.

* Everything is an “impl Trait”. This is closest to templated C++, but with much better ergonomics.

So, while I think I agree with your specific statement that the improved memory management may only be fully appreciated by those that cut their teeth on C’s segfaults and dangling pointers, I don’t think that’s the only benefit of Rust as a language.

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> * Everything is a Box<Rc<T>>. This is closest to dynamic garbage-collected languages, but with vastly improved performance.

Wait, reference counting everything all the time is faster than normal garbage collection?

I think more importantly it is reference counting across threads, meaning mutexes and breaking memory barrier with large performance penalty.

I believe you're discussing 'Arc'. 'Rc' is not thread safe.

then this is not "closest to GC languages", since GC langs usually provide memory management with respect to concurrency.

It's probably slower, but unlike normal GCed languages, it's not actually anywhere close to everything.

Many garbage collectors (e.g. CPython’s) will use reference counting as part of the process. If a reference count hits zero, the object can be destructed, prolonging the time between mark-and-sweep passes.

The performance difference, though, is mainly in switching over to a compiled language in the first place.

> Everything is a Box<Rc<T>>. This is closest to dynamic garbage-collected languages, but with vastly improved performance.

Why the `Box`?

Mostly to mimic the data structures allowed in languages where objects are held by reference. In Python, I could write a tree structure as `namedtuple(“node”, [“lhs”, “rhs”])`. If I tried to write a similar structure in Rust as `enum Node{Leaf, Branch(Node, Node)}`, the compiler rightfully complains that it would have an infinite size. But the indirection introduced by Box would let it be stored as `enum Node{Leaf, Branch(Box<Node>, Box<Node>)}`.

I think what the previous poster is pointing out is that Box<Rc<Foo>> is an unnecessary double indirection.

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