Daily Kotlin - 동기화, inline 함수, 익명함수, 확장 함수, 중위함수, if, when-in, for, inlineLambda return

• 공유 자원 보호

package chap03.section4

import java.util.concurrent.locks.ReentrantLock

var sharable = 1

fun main() {
    val reLock = ReentrantLock()

    //공유자원 접근 보호
    lock(reLock, ::criticalFunc)

    println(sharable)
}

fun criticalFunc() {
    sharable += 1
}

fun <T> lock(reLock: ReentrantLock, body: () -> T): T {
    reLock.lock()
    try {
        return body()
    } finally {
        reLock.unlock()
    }
}

• inline function

package chap03.section5

fun main() {
    shortFunc(3) {println("First call: $it")}
    shortFunc(5) {println("Second call: $it")}
}

inline fun shortFunc(a: Int, out: (Int) -> Unit) {
    println("Before calling out()")
    out(a)
    println("After calling out()")
}

Before calling out()
First call: 3
After calling out()
Before calling out()
Second call: 5
After calling out()

• 익명 함수 리턴

package chap03.section5.localreturn

fun main() {
    shortFunc(3) {
        println("First call: $it")
        return
    }
}

inline fun shortFunc(a: Int, out: (Int) -> Unit) {
    println("Before calling out()")
    out(a)
    println("After calling out()")
}

Before calling out()
First call: 3

• 확장 함수

package chap03.section5

fun main() {
    val source = "Hello World!"
    val target = "Kotlin"
    println(source.getLongString(target))
}

fun String.getLongString(target: String): String = if(this.length > target.length) this else target

• 중위 함수

package chap03.section5

fun main() {
    val multi = 3 multiply 10
    println("multi: $multi")
}

infix fun Int.multiply(x: Int): Int = this * x

• if

package chap04.section1

fun main() {
    val a = 12
    val b = 7

    val max = if(a > b) {
        println("a 선택")
        a
    } else {
        println("b 선택")
        b
    }

    println(max)
}

• else if

package chap04.section1

fun main() {
    print("Enter the score: ")
    val score = readLine()!!.toDouble()
    var grade: Char = 'F'

    if (score >= 90.0) {
        grade = 'A'
    } else if(score >= 80.0) {
        grade = 'B'
    } else if(score >= 70.0) {
        grade = 'C'
    }

    println("Score: $score Grade: $grade")
}

• when, in

package chap04.section1

fun main() {
    print("Enter the score: ")
    val score = readLine()!!.toDouble()
    var grade: Char = 'F'

    when(score) {
        in 90.0..100.0 -> grade = 'A'
        in 80.0..89.9 -> grade = 'B'
        in 70.0..79.9 -> grade = 'C'
        !in 70.0..100.0 -> grade = 'F'
    }
    println("score: $score grade : $grade")
}

Enter the score: 94
score: 94.0 grade : A

• for

while이랑 do-while은 일반적인 JAVA와 동일

package chap04.section2

fun main() {
    print("Enter the lines: ")
    val n = readLine()!!.toInt()

    for (line in 1..n) {
        for (space in 1..(n-line)) print(" ")
        for (star in 1..(2*line-1)) print("*")
        println()
    }
}

• inlineLambda return

package chap04.section3

fun main() {
    retFunc()
}

inline fun inlineLambda(a: Int, b: Int, out: (Int, Int) -> Unit) {
    out(a, b)
}

fun retFunc() {
    println("start of retFunc")
    inlineLambda(13, 3) { a, b ->
        val result = a + b
        if(result > 10) return
        println("result : $result")
    }
    println("end of retFunc")
}

start of retFunc