How do I call extension methods from outside the class they are defined in?

Question

Here is a minimal example that demonstrates the problem:

abstract class Base {
    abstract fun String.extension(x: Char)
}

class Derived : Base() {
    ove         


        

Answer 1

To decale an extension method outside the class using it, you should NOT implement it inside a class, and you should do like this:

package com.sample.test

import java.io.File

fun File.folderLength() : Long {
    return 0L
}

So in your class that call this method:

package com.sample.util

import com.sample.test.*
import java.io.File

class foo{
    fun getFolderSize(url: String) : Long{
        var file = new File("...")
        var length = file.folderLength()
        return length
    }
}

Hope this should help you.