Constructor visibility restricted to file

Question

I want to create an easier way to handle SharedPreferences. The way I want to call it is like this

get preference:

val email = SharedPrefs.userdata.email
val wifiOnly = SharedPrefs.connections.wifiOnly

set preference:

SharedPrefs.userdata.email = "someone@example.com"
SharedPrefs.connections.wifiOnly = true

I'm able to do so like this:

App.instance returns a Context object in the following snippet

object SharedPrefs {

    val userdata by lazy { UserPreferences() }
    val connections by lazy { ConnectionPreferences() }

    class UserPreferences {

        private val prefs: SharedPreferences = App.instance.getSharedPreferences("userdata", Context.MODE_PRIVATE)

        var email: String
            get() = prefs.getString("email", null)
            set(value) = prefs.edit().putString("email", value).apply()
    }

    class ConnectionPreferences {

        private val prefs: SharedPreferences = App.instance.getSharedPreferences("connections", Context.MODE_PRIVATE)

        var wifyOnly: Boolean
            get() = prefs.getBoolean("wifiOnly", false)
            set(value) = prefs.edit().putBoolean("wifyOnly", value).apply()
    }

}

The problem is that this can still be called: SharedPrefs.UserPreferences() Can I make this constructor private to this file or object only?

Answer 1

You can separate the interface and the implementation class, and make the latter private to the object:

object SharedPrefs {
    val userdata: UserPreferences by lazy { UserPreferencesImpl() }

    interface UserPreferences {
        var email: String
    }

    private class UserPreferencesImpl : UserPreferences {
        private val prefs: SharedPreferences = 
            App.instance.getSharedPreferences("userdata", Context.MODE_PRIVATE)

        override var email: String
            get() = prefs.getString("email", null)
            set(value) = prefs.edit().putString("email", value).apply()
    }


    // ...
}

Alternatively, if you are developing a library or you have a modular architecture, you can make use of the internal visibility modifier to restrict the visibility to the module:

class UserPreferences internal constructor() { /* ... */ }