[Larrikin]

I use extension functions on classes I don't own to add functionality I think the class should have had or would be extremely useful for my project if a certain type of class had the functionality. Your example would require a static utility class in Java or an object in Kotlin to use every where, the extension functions can just be inside of a kotlin file.

So the difference would be in Kotlin

  object StringUtilClass() {
    fun shout(s: String) = s + "!!!""
  }

  import StringUtilClass.*
  StringUtilClass.shout("I'm mad")

vs

  fun String.shout() = this + "!!!"

  import StringExtensions.*
  "I'm mad".shout()

Kotlin doesn't always add brand new functionality, it also strives to make it faster to read and write code.

[fauigerzigerk]

That surprises me. I would have thought that you could do this in Kotlin just as you can in Java with static import:

  import StringUtilClass.*
  shout("I'm mad")

[Larrikin]

Personally I find that less clear where shout is coming from and how to use it. It would also make autocomplete less useful as mentioned