Can't comment selection

Question

Sometimes, it seems I can\'t comment my code with the usual shortcut (command + /) under Xcode 8 Beta 4. The option is disabled in the menu (screen

Answer 1

My situation is a bit different(stupid?): I found I can't comment any line from a particular part of a particular file. I tried all the methods above with Xcode 8.1 and Xcode 8.2, but got no luck. Finally I found it was caused by a comment trick like below,

1 /*
2 code 
3 //*/
4 code

In Xcode, you can't comment line 2 with Cmd+/ because it has been commented already by /**/, which is fine. However, you can't even comment line 4 with Cmd+/, as Xcode may think it's still in a /* */ block, but it's actually not. If I remove // from line 3, then commenting line 4 works fine.