Pass Parameters to Scala Object

Question

Is it ever possible to initialize a Scala object from an external object? The Scala object that I'm trying to initialize does not have any Companion class. Here it is as an example:

object ObjectA {
  val mongoDBConnectionURI = // This is the Val that I want to initialize from an external object
  ....
  ....
}

But the mongoDBConnectionURI which is of type MongoDBConnectionURI needs a host and a port that I have to read from a config file which is actually done by Object B and these values are passed to ObjA. Later all my DAO objects will access the mongoDBConnectionURI variable in Object A to get the connection string. How could I pass the values from Object B to Object A and have the vals in Object A initialized?

That does not work. The initialization logic that reads the values for the db credentials resides in another project and this another project which is a play application, on startup reads the config details and sends them to the ObjectA which is added as a dependency to the play project. The DAO classes that access the database reside in this dependency and they are not supposed to have any references back to ObjectB. — joesan
– joesan, Commented Mar 17, 2014 at 15:49
i believe you are looking for the Factory pattern. en.wikipedia.org/wiki/Factory_method_pattern — Rob Starling
– Rob Starling, Commented Mar 17, 2014 at 16:59

dk14 · Accepted Answer · 2014-06-11 13:39:16Z

6

Simple solution:

object ObjectA {
  lazy val mongoDBConnectionURI = getConnection(name.get, passwd.get)
  var name: Option[String] = None
  var passwd: Option[String] = None
}

If you use mongoDBConnectionURI after "passing" name and password - everything should work fine. But i'd recommend to use class instead of object and pass it to the DAO classess (also without cyclic references):

==moduleA==

class UserDAO(objectA: ObjectA) 

==moduleB==

object ObjectB {
  val user = ...
  val passwd = ...
  val a = new ObjectA(name, passwd)
  object UserDAOInstance extends UserDAO(a)

}

edited Jun 11, 2014 at 13:39

answered Jun 10, 2014 at 20:30

dk14

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