I was having problems with Xcode 8. It was turning my Mac into a brick. There is a HUGE memory leak currently which will halt your system (Xcode was using 38 gigs of memory at one point…and I only have 16 physical gigs). Then I downgraded to 7.3 but auto complete and coloring wasn’t working. So I went down to 7.2.1 and everything is fine. I lost a week of learning because of this and just incase anyone is going thru the same problems I hope it helps. I will be staying on 7.21 until I read that they have plugged the memory leak in 8.
Oh dear Apple. New XCode releases always spell trouble.
I am using iCloud to save my projects so I can use them in multiple locations. I changed my derived data directory to relative to workspace in Xcode so I don’t have to index every time. Is this the right way to do that?
That would certainly work.
Just an FYI for any Mac/XCode users. The Xcode 8.1 version has fixed the memory leak 
and it seems to be a bit quicker at indexing (like 200 times faster!) and compiling is much faster too.