# Kotlin Tour

joow
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## Lambdas and Collections

### Higher-order functions

https://kotlinlang.org/docs/reference/lambdas.html#higher-order-functions

A higher-order function is a function that either :

``````- takes at least one function as argument
- returns a function
``````

### Lambda expressions

https://kotlinlang.org/docs/reference/lambdas.html#lambda-expressions-and-anonymous-functions

The formal syntax for lambda expression is :

``````val sum = { x: Int, y: Int -> x + y }
``````

We can also rewrite the previous expression like this :

``````val sum: (Int, Int) -> Int = { x, y -> x + y }
``````

If the compiler can infer the signature you can leave out the signature :

``````ints.filter { it > 0 }
``````
Declare a function negate that takes a predicate and returns its opposite

### Destructuring Lambdas

https://kotlinlang.org/docs/reference/multi-declarations.html#destructuring-in-lambdas-since-11

Since Kotlin 1.1 it is possible to destruture lambdas.

Given a map of countries and their capital, create a function capital printing for each entry "The capital of ... is ..."

### Collections

https://kotlinlang.org/docs/reference/collections.html

Kotlin has immutable and mutable collections :

``````// List
val mutableList = mutableListOf("Java", "Kotlin", "JavaScript")
val immutableList = listOf("Java", "Kotlin", "JavaScript")
immutableList.plus("Go") // returns a new list
// Set
val mutableSet = mutableSetOf(1, 3, 5, 7, 9)
val immutableSet = setOf(0, 2, 4, 6, 8)
immutableSet.plus(10) // returns a new set
// Map
val mutableMap = mutableMapOf("1" to 1, "2" to 2, "3" to 3)
mutableMap.put("4", 4)
val immutableMap = mapOf("1" to 1, "2" to 2, "3" to 3)
immutableMap.plus("4" to 4) // returns a new map
``````

#### Fun with numbers

Generate the ten first numbers and print them
Generate the first ten powers of two and print them
Print the first power of 2 greater than 10000

#### Fun with data

Print the birth countries of the musicians, without duplicate
Generate a string containing the last names of the musicians, sorted in ascending order and separated by a comma
Count the number of musicians having their last name containing the letter B, no matter the case
Print the list of death countries and the number of deceased musicians
Print the musicians ordered by their death age. Who was the youngest and who was the oldest ?
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