Question: XCode 6 Beta 5 and autocomplete stopped working. I thought problem in Beta 5 but I've reinstall to Beta 4 and it's still not work but it did before. I check preferences for "suggests" and I tried to delete Derived Data but it doesn't help

Answer: 
I found the solution. Problem was in an array.
I have big array like: 
`let array:[NSString] = ["first","second"...]`
 I changed it to 
`var array = ["first","second"...]`
I don't why it's happened but it works. It was so hard to find the problem.
I was having this problem. 

This is what worked for me. 

1. Clear derived data.

Window -> Organizer -> "Select you project" -> Delete Derived Data. 

2. Clean the project
3. Quit Xcode ----- this is very important. You might have to restart you computer.
4. Open Xcode again

Hope this works for you. This worked on 2/9/2015