xcode - Cannot import Firebase or FirebaseDatabase into multiple classes in iOS -

i have installed firebase , firebasedatabase project using cocoapods describe on site. on 1 viewcontroller have firebasedatabase imported , seems fine there, when try import firebasedatabase onto class, starts glitch , throw compiler errors in both classes.

for example, if have firebasedatabase imported only viewcontroller1, works fine:

import uikit import firebasedatabase  class viewcontroller1: uiviewcontroller {     let classref = firdatabase.database().reference().child("someclass")     ... } 

but if import 1 other class or more, same code, throws errors like:
use of unresolved identifier 'firdatabase'
, on other types or functions have firebasedatabase.
throw: command failed due signal: segmentation fault: 11
if try remove import statement other class still glitch time , i'd have build project couple of times until builds successfully.

another thing have noticed when try import firebase modules, if have imported them once in other class, modules displayed strikethrough, in here: (if matters)

i have tried reinstall pods , clean deriveddata folder nothing helps.
problem?

make sure created file (cocoa touch / etc.) while working in xcworkspace. if working in regular xcodeproj, cocoapod wont translate