Kotlin Programming Cookbook

How it works…

The sortedBy function is syntactic sugar provided by Kotlin. Internally, it's calling the sortedWith method that takes in a comparator.

Now, let's see the implementation of the sortBy function:

public inline fun <T, R : Comparable<R>> Iterable<T>.sortedBy(crossinline selector: (T) -> R?): List<T> {    return sortedWith(compareBy(selector))}

The sortBy function calls the sortedWith method inside it, which is as following:

public fun <T> Iterable<T>.sortedWith(comparator: Comparator<in T>): List<T> {    if (this is Collection) {       if (size <= 1) return this.toList()       @Suppress("UNCHECKED_CAST")       return (toTypedArray<Any?>() as Array<T>).apply { sortWith(comparator) }.asList()    }    return toMutableList().apply { sortWith(comparator) }}