Xcode 9 Autocomplete Not Working 100% - Partially Working

Deleting the DERIVED DATA folder seemed to fix my issue. Thanks to this post: swift println() not showing autocomplete options while writting code

Try:

1. Go to Xcode > Preferences > Text Editing
2. Under Code completion - Uncheck 'Suggest completions while typing'
3. Quit out of Xcode and then relaunch Xcode.
4. Go to Xcode > Preferences > Text Editing again
5. Quit out of Xcode and then relaunch Xcode.
6. Now go to Code completion and check 'Suggest completions while typing'.
7. Try typing library function or enum and enjoy!