How could a “global implicit class” be defined in Scala?

Question

Considering that a implicit class "must be defined inside of another trait/class/object" 1 , how can a implicit conversion be defined globally?

The case is that I'd like to add a method to all Strings (or Lists ) in my application, or at least to several packages of it.

Answer 1

One cannot add anything to the "global" scope, neither in Java, nor in Scala. However, in Scala one can define package objects , which can contain methods that are used all over the package, and can be easily imported by the user.

This looks something like this: in the directory foo/bar/baz one creates a file called package.scala with the following content:

package foo.bar

package object baz {
  implicit def incrediblyUsefulConversion(s: String) = ...
}

The user then can do the following in his code to activate the conversion:

import foo.bar.baz._

or maybe

import foo.bar.baz.incrediblyUsefulConversion

Of course, you can also use your own code in other packages, just like any other user.