I think they had to go with ARC due to the requirement that swift interoperates with Objective-C. If that hadn't been a constraint, yeah it would be an interesting decision.
No - they already had GC working with Objective-C and could have chosen it for swift if they had thought it was the best technology.
Here's a quote from Chris Lattner:
"GC also has several huge disadvantages that are usually glossed over: while it is true that modern GC's can provide high performance, they can only do that when they are granted much more memory than the process is actually using. Generally, unless you give the GC 3-4x more memory than is needed, you’ll get thrashing and incredibly poor performance. Additionally, since the sweep pass touches almost all RAM in the process, they tend to be very power inefficient (leading to reduced battery life).
I’m personally not interested in requiring a model that requires us to throw away a ton of perfectly good RAM to get an “simpler" programming model - particularly on that adds so many tradeoffs."
Yes, they had GC working with Objective-C but there were so many problems with it that they dropped the GC in favor of ARC years ago. By the time Swift came along, GC with Objective-C was no longer an option.
Chris Lattner was already working on Swift when the decision to drop GC was made. Guess who made the decision? Chris Lattner. If anything, GC was dropped because of Swift, not the other way around.
