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#kotlin #tips

참고 자료

Kotlin by Jetbrains on Youtube - playlist 『Kotlin Tips 2023』

1. How to Improve Loops in Kotlin | Kotlin Tips 2023¶

val fruits = listOf("Apple", "Banana", "Cherry", "Durian")

Step 0

basic loops with .. range

fun main() {
    for (index in 0 .. fruits.size - 1){
        val fruit = fruits[index]
        println("$index: $fruit")
    }
}

Step 1

basic loops with until range

fun main() {
    for (index in 0 until fruits.size){
        val fruit = fruits[index]
        println("$index: $fruit")
    }
}

Step 2

loops with Collection.lastIndex

fun main() {
    for (index in 0 .. fruits.lastIndex){
        val fruit = fruits[index]
        println("$index: $fruit")
    }
}

Step 3

loops with Collection.indices

fun main() {
    for (index in fruits.indices){
        val fruit = fruits[index]
        println("$index: $fruit")
    }
}

Step 4

loops with Collection.withIndex()

fun main() {
    for ((index, fruit) in fruits.withIndex()){
        println("$index: $fruit")
    }
}

=== eoc

2. How YOU CAN DO MORE with the Elvis Operator | Tips from the Kotlin Team¶

Elvis 연산자 기본

Elvis 연산자 기본 활용

fun main() {
    val name :String? = getName()
    val gretting : String = name ?: "undefined"
}

Elvis 연산자 with run { }

Elvis 연산자 는 Expression 만 받으면 된다.

fun main() {
    val name :String? = getName()
    val gretting : String = name ?: run { // (1)
        println("oops no name defined")
        "undefined"
    }
}

run 을 통해 람다 블럭을 expression 으로 제공할 수 있다.

=== eoc

3. These 3 Tips Will Change Your Approach to Strings in Kotlin¶

fun main(){
    //tip1
    println("momo_dancing.jpg".removeSuffix(".jpg")) // momo_dancing
    println("__MEOW__".removeSurrounding("__")) // MEOW

    //tip2
    println("".isEmpty()) // true
    println(" ".isBlank()) // true

    //tip3
    println("momo".equals("MomO", ignoreCase = true)) // true
}

4. Calculate Your Code Performance | Kotlin Tips 2023¶

import kotlin.time.ExperimentalTime
import kotlin.time.measureTimedValue

@OptIn(ExperimentalTime::class)
fun main() {
    val (value, time) = measureTimedValue { longOperation() }
    println("It took $time to calculate $value")
}

5. Deduplicating Collection Items | Kotlin Tips 2023¶

컬렉션 중복 제거

val fruitBasket = listOf("Apple", "APPLE", "ApPle", "Banana", "Melon", "Apple")

fun main() {
    println(fruitBasket.distinct()) // (1)
    println(fruitBasket.toSet()) // (2)
    println(fruitBasket.distinctBy { it.toLowerCase() } ) // (3)
}

[Apple, APPLE, ApPle, Banana, Melon] - List<String>
[Apple, APPLE, ApPle, Banana, Melon] - Set<String>
[Apple, Banana, Melon] - List<String> - List<String>

Last update: February 26, 2023
Created: February 20, 2023