Publishers in Combine are usually passed by value, since they are structs; however, you can use the built in Combine operator share() to pass them by reference, establishing one true subscription and simply sharing the data with other subscribers as they come along. Want to wait until all of the subscribers are ready before starting the data flow? multicast() allows you to do just that, and start the data when you are ready.
This is a companion discussion topic for the original entry at https://www.raywenderlich.com/21773708-intermediate-combine/lessons/2