That goes for manual memory management -- and certainly languages with a reference-counting GC, like Rust -- as well. The main difference is by far footprint overhead.
It's a mistake to say that the Rust language has reference counting. There's a pair of reference-counting wrapper types in its standard library (Rc and Arc), or you can roll your own, but there's no special support for these types in the language, and their use is optional. Most of the time, you won't be using these reference-counting types. Box (the generic heap-allocated or "boxed" type) doesn't use reference counting. String (and its several specialized variants) doesn't use it. Vec (the generic heap-allocated array type) doesn't use it. HashMap, HashSet, BTreeMap, BTreeSet, none of them use reference counting. And so on. You can write a lot of Rust code without using reference counting even once.
What the Rust language has is just C++-style RAII: when a value goes out of scope, if it implements Drop, its Drop::drop is called.
Having these types in the standard library is the language having those types.
Perhaps it's not integrated to the level that a language like swift is. However, I think it's reasonable to say the language supports Rc when the standard library supports it. I'd say the same thing about C++ with `shard_ptr`.
Otherwise you end up in weird pedantic notions about what a language has or does not have. Does C have a heap? Well, technically no since malloc and free are just function calls in the standard library and you can write valid C programs without calling those functions.
It depends on whether you consider the standard library an indivisible part of the language or not. For Rust, it's clearly not the case, since you have the #![no_std] mode in which only a subset of the standard library is available, and this subset does not include these reference counted wrapper types (or any heap-allocated type at all).
> Perhaps it's not integrated to the level that a language like swift is. However, I think it's reasonable to say the language supports Rc when the standard library supports it. I'd say the same thing about C++ with `shard_ptr`.
It's one thing to say a language "supports reference counting", which only means you can use reference counting with it, and another thing to say "[...] languages with a reference-counting GC", which implies that the language uses a GC for everything, and that GC is a reference-counting GC.
> Does C have a heap? Well, technically no since malloc and free are just function calls in the standard library and you can write valid C programs without calling those functions.
It's actually the same thing: C can run on either a "hosted" environment or a "freestanding" environment, and on the later, most of the standard library is not available, including malloc and free. So C does not necessarily have a heap when running on a freestanding environment.
It would still be available in a #![no_std] environment using `extern crate alloc`.
This crate generally abstracts over the concept of allocation too, so relying on it doesn't require you to also have an allocator - it just requires someone at some point specify one with #[global_allocator]
It is not, if you have objects with dynamic lifetimes, and allocating them for the whole duration of the program is not an option.
Sure, their use can be much less than a managed language that can only do automatic memory management, but RC is objectively a worse from most perspective than tracing GC, except for the fact that they don’t need runtime support, and a slightly lower memory overhead.
With properly architected code, the times you need to use rc are extremely small.
3x to 100x is not „slightly” in my dictionary.
The point of manual memory management is to come up with problem-specific strategies to avoid or at least reduce dynamic memory allocation, not to insert manual release/free calls for individual objects ;)
...while I agree, for many C++ and Rust coders statements like this are pure heresy ;)
It's a matter of definitions. For many people, "garbage collection" refers only to tracing GC, and reference counting is a separate category. In my experience, that's the common usage; insisting that "reference counting is formally (in some paper from the last century) also defined as a form of GC" will not magically change the opinions "many C++ and Rust coders" have about tracing GC. In fact, I'd say that insisting on this nomenclature point only weakens the whole argument; tracing GC should stand on its own merits, and not on depend on some nomenclature equivalence to be accepted (if quibbling about nomenclature is your strongest argument, your arguments are weak).
Tracing GCs have clearly proven themselves and are everywhere (JVM, CLR, Go, Dart, OCaml, etc.) but we can't ignore that the Apple ecosystem (Swift) is using ARC. That's a significant share of the "market". Python and Ruby also use reference counting, but I don't think anyone is considering them state-of-the-art GC.
> Tools to automate the “actually freeing the memory” part, like lifetimes in Rust and RAII in C++, don’t solve these problems. They absolutely aid correctness, something else you should care deeply about, but they do nothing to simplify all this machinery.
You can opt into reference counting with `std::rc::Rc`. (You can even opt into mark-and-sweep GC using the `gc` crate, but this isn't done much...).
I agree with pron’s larger point. GC is fine for most applications. It’s just factually inaccurate to compare Rust’s memory management with languages like Python and PHP.