import Foundation

public enum PusherHost {
    case host(String)
    case cluster(String)

    public var stringValue: String {
        switch self {
        case .host(let host): return host
        case .cluster(let cluster): return "ws-\(cluster).\(Constants.API.pusherDomain)"
        }
    }
}

import Foundation

public enum PusherHost {
    case host(String)
    case cluster(String)

    public var stringValue: String {
        switch self {
        case .host(let host): return host
        case .cluster(let cluster): return "ws-\(cluster).pusher.com"
        }
    }
}

--- 
+++ 
@@ -7,7 +7,7 @@
     public var stringValue: String {
         switch self {
         case .host(let host): return host
-        case .cluster(let cluster): return "ws-\(cluster).pusher.com"
+        case .cluster(let cluster): return "ws-\(cluster).\(Constants.API.pusherDomain)"
         }
     }
 }
Replace string literal for domain with Constants static member
