Arc isn't really garbage collection. It's like a reference counted smart pointer like C++ has shared_ptr.
If you drop an Arc and it's the last reference to the underlying object, it gets dropped deterministically.
Garbage collection generally refers to more complex systems that periodically identify and free unused objects in a less deterministic manner.
No, this is a subset of garbage collection called tracing garbage collection. "Garbage collection" absolutely includes refcounting.
Chapter 5, https://gchandbook.org/contents.html
Other CS quality references can be provided with similar table of contents.
As a rough approximation, if you're very heavy-handed with ARC then you probably shouldn't be using rust for that project.
[0] The term "leak" can be a bit hard to pin down, but here I mean something like space which is allocated and which an ordinary developer would prefer to not have allocated.
However, I disagree with generalizations that you can judge the quality of code based on whether or not it uses a lot of Arc. You need to understand the architecture and what's being accomplished.
That wasn't really my point, but I disagree with your disagreement anyway ;) Yes, you don't want to over-generalize, but Arc has a lot of downsides, doesn't have a lot of upsides, and can usually be relatively easily avoided in lieu of something with a better set of tradeoffs. Heavy use isn't bad in its own right, but it's a strong signal suggestive of code needing some love and attention.
My point though was: If you are going to heavily use Arc, Rust isn't the most ergonomic language for the task, and where for other memory management techniques the value proposition of Rust is more apparent it's a much narrower gap compared to those ergonomic choices if you use Arc a lot. Maybe you have to (or want to) use Rust anyway for some reason, but it's usually a bad choice conditioned on that coding style.
If you need a referecne counted garbage collector for more than a tiny minotiry of your code, then Rust was probably the wrong choice of language - use something that has a better (mark and sweep) garbage collectors. Rust is good for places where you can almost always find a single owner, and you can use reference counting for the rare exception.
However, the difference between Arc and a Garbage Collector is that the Arc does the cleanup at a deterministic point (when the last Arc is dropped) whereas a Garbage Collector is a separate thing that comes along and collects garbage later.
> If you need a referecne counted garbage collector for more than a tiny minotiry of your code
The purpose of Arc isn't to have a garbage collector. It's to provide shared ownership.
There is no reason to avoid Rust if you have an architecture that requires shared ownership of something. These reductionist generalizations are not accurate.
I think a lot of new Rust developers are taught that Arc shouldn't be abused, but they internalize it as "Arc is bad and must be avoided", which isn't true.
That is the most common implementation, but that is still just an implementation detail. Garbage collectors can run deterministically which is what reference counting does.
> There is no reason to avoid Rust if you have an architecture that requires shared ownership of something.
Rust can be used for anything. However the goals are still something good for system programming. Systems programming implies some compromises which makes Rust not as good a choice for other types of programming. Nothing wrong with using it anyway (and often you have a mix and the overhead of multiple languages makes it worth using one even when another would be better for a small part of the problem)
> I think a lot of new Rust developers are taught that Arc shouldn't be abused, but they internalize it as "Arc is bad and must be avoided", which isn't true.
Arc has a place. However most places where you use it a little design work could eliminate the need. If you don't understand what I'm talking about then "Arch is bad and must be avoided" is better than putting Arc everywhere even though that would work and is less effort in the short run (and for non-systems programming it might even be a good design)
Large scale teams always get pointer ownership wrong.
Project Zero has enough examples.
Reference counting is a valid form of garbage collection. It is arguably the simplest form. https://en.wikipedia.org/wiki/Garbage_collection_(computer_s...
The other forms of GC are tracing followed by either sweeping or copying.
> If you drop an Arc and it's the last reference to the underlying object, it gets dropped deterministically.
Unless you have cycles, in which case the objects are not dropped. And then scanning for cyclic objects almost certainly takes place at a non-deterministic time, or never at all (and the memory is just leaked).
> Garbage collection generally refers to more complex systems that periodically identify and free unused objects in a less deterministic manner.
No. That's like saying "a car is a car; a vehicle is anything other than a car". No, GC encompasses reference counting, and GC can be deterministic or non-deterministic (asynchronous).
In c++ land this is very often called garbage collection too
