Kotlin Extension Methods Extension functions to Companion Objects (appearance of Static functions)
Example
If you want to extend a class as-if you are a static function, for example for class Something add static looking function fromString, this can only work if the class has a companion object and that the extension function has been declared upon the companion object:
class Something {
companion object {}
}
class SomethingElse {
}
fun Something.Companion.fromString(s: String): Something = ...
fun SomethingElse.fromString(s: String): SomethingElse = ...
fun main(args: Array<String>) {
Something.fromString("") //valid as extension function declared upon the
//companion object
SomethingElse().fromString("") //valid, function invoked on instance not
//statically
SomethingElse.fromString("") //invalid
}
