The Kotlin collections framework is full of interesting features that make it stand apart from the collections frameworks in other languages, such as Java. You already been introduced to some of those features, such as separate interfaces for read-only and mutable collections, square box operator, such as arrays, and so on. What I'm going to introduce now is probably the most interesting feature of the Kotlin collections framework—data operation (extension) functions.
Kotlin supports data operation (extension) functions for all of its collections framework interfaces. Now, what are data operation functions? They are extension functions by which we can access/process or operate on data from a collection. If you are familiar with the ReactiveX framework (for example, RxJava or RxKotlin) or any of the Reactive streams framework...
