[swift-evolution] What about garbage collection?

Dave Abrahams dabrahams at apple.com
Mon Feb 8 14:45:26 CST 2016

on Mon Feb 08 2016, FĂ©lix Cloutier <swift-evolution at swift.org> wrote:

> Has there been a garbage collection thread so far? I understand that
> reference counting vs. garbage collection can be a heated debate, but
> it might be relevant to have it.
> It seems to me that the two principal upsides of reference counting
> are that destruction is (essentially) deterministic and performance is
> more easily predicted. However, it comes with many downsides:
> object references are expensive to update
> object references cannot be atomically updated
> heap fragmentation
> the closure capture syntax uses up an unreasonable amount of mindshare
> just because of [weak self]
> Since Swift doesn't expose memory management operations outside of
> `autoreleasepool`, it seems to me that you could just drop in a
> garbage collector instead of reference counting and it would work (for
> most purposes).
> Has a GC been considered at all?

Yes.  Among other problems, you can't do copy-on-write efficiently with
a GC, because you can't detect a unique reference.  And without
efficient copy-on-write, most interesting value types (Array) are out
the window.


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