[vsgherzi]

No has seemed to call it out yet but swift uses a form of garbage collection but remains relatively fast. I was against this at first but the more I think about it, I think it has real potential to make lots of hard problems with ownership easier to solve. I think the next big step or perhaps an alternative would be to make changes to restrictions in unsafe rust.

I think the pursuit of safety is a good goal and I could see myself opting into garbage collections for certain tasks.

[worik]

Swift uses reference counting

Slows down every access to objects as reference counts must be maintained

Something weird that I never bothered with to enable circular references

[marcianx]

Reference counted pointers can deference an object (via a strong pointer) without checking the reference count. The reference count is accessed only on operations like clone, destruction, and such. That being said, access via a weak pointer does require a reference count check.

[fulafel]

This sounds different from common refcounting semantics in other languages, is it really so in Swift?

Usually access increases the reference count (to avoid the object getting GC'd while you use it) and weak pointers are the exception where you are prepared for the object reference to suddenly become invalid.

[Someone]

> Usually access increases the reference count

Taking shared ownership increases the reference count, not access.

[marcianx]

When you have a strong pointer, you already have a positive ref count. Only once the strong pointer is destructed, is the reference count decremented.

[Someone]

> Slows down every access to objects as reference counts must be maintained

Definitely not every access. Between an “increase refcount” and an “decrease refcount” you can access an object as many times as you want.

Also:

- static analysis can remove increase/decrease pairs.

- Swift structs are value types, and not reference counted. That means Swift code can have fewer reference-counted objects than similar Java code has garbage-collected objects.

It does perform slower than GC-ed languages or languages such as C and rust, but is easier to write [1] than rust and C and needs less memory than GC-ed languages.

[1] The latest Swift is a lot more complex than the original Swift, but high-level code still can be reasonably easy.