learning kotlin synthax

learn_kotlin.kt

/**
 * You can edit, run, and share this code.
 * play.kotlinlang.org
 */
fun main() {
    val amount = 90
    
    when (amount) {
        in 1..10 -> println("in between one and ten")
        !in 11..20 -> println("not in between 11 and 20")
        125 -> println("is 124")
        else -> {
            println("default case")
        }
    }
    println(calculateCatAge(1))
    println(calCatAgeLamda(1))
    showName("Bolaji")
    
    // in kotlin when the last argument in a function is 
    // another function, it allows you pass the function 
    // arg as a lambda outside of the argument declaration
    // brace
    enhancedMessage("Hello Paulo") {
        add(12, 12)
    }
    enhancedMessage("Hello Paulo") { 12 }
    
    // This is an immutable list. `listOf` lists cannot be mutated
    val myListOfNames = listOf("James", "Paul", "Rafael", "Gina")
    println(myListOfNames)
    
    for (item in myListOfNames) {
        println("$item <====")
    }
    
    myListOfNames.forEach { it ->
        println("$it in for each")
    }
    
    val myMutableList = mutableListOf(12, 40, 34)
    myMutableList.add(45)
    
    println(myMutableList)
    println("Number of elements: ${myMutableList.size}")
    println("Second element: ${myMutableList[1]}")
    
    // this is immutable
    val mySet = setOf("US", "MZ", "AU")
    println(mySet)
    
    val myMutableSet = mutableSetOf(1,3,4,5)
    myMutableSet.add(8)
    myMutableSet.add(3)
    println(myMutableSet)
    
    // Maps
    // immutable map
    val secretMap = mapOf(
    	"Up" to 1,
        "Down" to 2,
        "Left" to 3,
        "Right" to 4
    )
    println(secretMap)
    println("all keys: ${secretMap.keys}")
    println("all keys: ${secretMap.values}")
    if ("Up" in secretMap) println("Up is in!")
    
    val myMutableSecretMap = mutableMapOf(
    	"One" to 1,
        "Two" to 2,
        "Three" to 3
    )f
    myMutableSecretMap.put("Four", 4)
    myMutableSecretMap["Five"] = 5
    println(myMutableSecretMap)
    
    val myNewList = mutableListOf<String>()
    myNewList.add("Soso")
    
    // empty collections
    val empty = emptyList<String>()
    val emptySet = emptySet<String>()
    val emptyMap = emptyMap<String, Boolean>()
}

fun calculateCatAge(age: Int): Int = age * 7
val calCatAgeLamda: (Int) -> Int = { age -> age * 7 }

// unit means void in Kotlin
// in a lambda you don't always need to specify the arg, it's available as `it`
val showName: (String) -> Unit = { println(it)}

val add: (Int, Int) -> Int = { a, b -> a + b }

// trailing lambda
fun enhancedMessage(message: String, funAsParameter: () -> Int) {
    println("$message ${funAsParameter()}")
}