internal and Modules

A module is a set of Kotlin files compiled together: a Gradle module (e.g. :app, :core:network), a Maven project, or an IntelliJ module. internal code can be used anywhere inside that module but is hidden from other modules.

:core:network module                 :app module
---------------------------          ------------------------
internal class HttpEngine     --X-->  cannot see HttpEngine
public  class ApiClient       ----->  can use ApiClient

// In module :core:network
internal class HttpEngine {             // implementation detail
    fun execute(url: String): String = "..."
}

class ApiClient {                        // public API of the module
    private val engine = HttpEngine()
    fun get(path: String) = engine.execute("https://api.example.com$path")
}