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Cristian Popescu
Cristian Popescu

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Kotlin and it's extenstions

Here are a few of my favourite shortcuts to work with Kotlin. If you have others, don't hesitate to mention them.

1. chunked doc

Works on Iterables that are most common to us, like Lists or Sequences.
It does exactly what it sounds like, splits a collection in equal parts (if possible) and enables us to transform each resulting sublist, all in the same operation.

val initialList = listOf("chair", "table", "couch")
val chunkedTwo = initialList.chunked(2)
// chunkedTwo -> [["chair", "table"], ["couch"]]
val transform = initialList.chunked(2) { subList -> subList.last() }
// transform -> ["table", "couch"]

You may have needed this or not, but it's nice to know it's there. Sometimes when you think about it, it's not that difficult to do, but reimplementing the same things may cause you to slip up somewhere, somehow.

2. with doc

Scoped functions like with enable us to write more verbose code. This one can cut down on the length of the line by scoping to a nested variable in your object. But I think an example is most fit here.

data class Birthday(val year: Int, val month: Int, val day: Int)
data class Person(val name: String, val birthday: BirthDay)
data class Employee(val position: String, val person: Person)

// having a method that receives an employee and computes a string
fun nameAndBirth(employee: Employee) = with(employee.person.birthday) {
    // in here, the scope is actually Birthday
    "${}: $day/$month/$year"

Another cool fact about with is that, like the other functions run, let and so on, it will return the last value that was computed. In our case, the String that contains the name and birth of the employee.

3. associateBy doc

This is a great shortcut to create maps for objects that you need to find later on, by certain keys (id, name, length and so on). You could find it really useful, since this, in many cases is repeatable.

data class Room(val id: Long, val name: String, val area: Double)

val rooms = listOf(Room(1, "living", 40.5), Room(2, "living", 39.3))
val associated = rooms.associateBy { }
// associated -> { "living"=Room(2, "living", 39.3)}
val associated2 = rooms.associateBy { }
// associated2 -> { 1=Room(1, "living", 40.5), 2=Room(2, "living", 39.3)}

Be careful since if two keys match, only the last one will be present in the resulted map.

Hope you can try these out if you didn't already.

Thanks for Reading

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