How to deal with a variable in a library that needs to be set outside of it?

I'm using Datomic in several projects and it's time to move all the common code to a small utilities library.

One challenge is to deal with a shared database uri, on which most operations depend, but must be set by the project using the library. I wonder if there is a well-established way to do this. Here are some alternatives I've thought about:

• Dropping the uri symbol in the library and adding the uri as an argument to every function that accesses the database

• Altering it via alter-var-root, or similar mechanism, in an init function

• Keeping it in the library as a dynamic var *uri* and overriding the value in a hopefully small adapter layer like

  (def my-url ...bla...)

  (defn my-fun [args] (with-datomic-uri my-uri (apply library/my-fun args))

• Keeping uri as an atom in the library