109: Learning Kotlin - Sequences the new Iterables

In this episode of Fragmented, we go back to learning some Kotlin and look at the Iterable like data structure introduced called "Sequences". What is a sequence? How is it different from Iterable? When should I use it? Show Notes Kotlin Sequence Java Iterable vs Iterator - stackoverflow.com Eager/Lazy Eager evaluation: val lst = listOf(1, 2) val lstMapped: List = lst.map { print("$it "); it * it } print("before sum ") val sum = lstMapped.sum() // prints "1 2 before sum" Lazy evaluation: val seq = sequenceOf(1, 2) val seqMapped: Sequence = seq.map { print("$it "); it * it } print("before sum ") val sum = seqMapped.sum() // prints "before sum 1 2" Source stackoverflow.com answer Intermediate and terminal operations Notice that at each chain operation, a new temporary list is created: data class Person(val name: String, val age: Int) fun main(args: Array) { val people = listOf(Person("Chris Martin", 31), Person("Will Champion", 32), Person("Jonny Buckland", 33), Person("Guy Berryman", 34), Person("Mhris Cartin", 30)) println(people .filter { it.age > 30 } // new temp. list .map { it.name.split(" ").map {it[0]}.joinToString("") } // new temp. list .map { it.toUpperCase() }) // new temp. list } Using a sequence: println(people .asSequence() // convert to sequence .filter { it.age > 30 } // lazy eval (intermediate op) .map { it.name.split(" ").map {it[0]}.joinToString("") } // lazy eval (intermediate op) .map { it.toUpperCase() } // lazy eval (intermediate op) .toList() // terminal operation ) Without a terminal operation, Sequences won't print anything: val seq = sequenceOf(1, 2, 3) println(seq) // prints address println(seq.toList()) // [1, 2, 3] You can't pick an index from a sequence: println(seq[0]) // throws ERROR "No get method providing array access" println(seq.toList()[0]) // 1 Sponsors Mapbox - Android developers don't have to settle for a default same-map-no-matter-what option in their Android app. Mapbox offers complete map design control, allowing you to create beautiful custom maps to meet the needs of your Android users. Check them out today at mapbox.com/android Contact @fragmentedcast [twitter.com] @donnfelker and +DonnFelker @kaushikgopal and +KaushikGopalIsMe