Using coroutines in real life

Microbenchmarks are very funny and they give us an idea of the power of Kotlin coroutines, but they don't represent a real-case scenario.

Let's introduce our real-case scenario:

enum class Gender {
   MALE, FEMALE;

   companion object {
      fun valueOfIgnoreCase(name: String): Gender = valueOf(name.toUpperCase())
   }
}

typealias UserId = Int

data class User(val id: UserId, val firstName: String, val lastName: String, val gender: Gender)

data class Fact(val id: Int, val value: String, val user: User? = null)

interface UserService {
   fun getFact(id: UserId): Fact
}

Our UserService interface has just one method—getFact will return a Chuck Norris-style fact about our user, identified by the user ID.

The implementation should check first on a local database for a user; if the user doesn't exist in the database, it should get it from...