When Expression trong Kotlin (Pattern Matching)

val day = 3
 
when (day) {
    1 -> println("Monday")
    2 -> println("Tuesday")
    3 -> println("Wednesday")
    4 -> println("Thursday")
    5 -> println("Friday")
    6 -> println("Saturday")
    7 -> println("Sunday")
    else -> println("Invalid day")
}

val day = 3
val dayName = when (day) {
    1 -> "Monday"
    2 -> "Tuesday"
    3 -> "Wednesday"
    4 -> "Thursday"
    5 -> "Friday"
    6 -> "Saturday"
    7 -> "Sunday"
    else -> "Invalid"
}
println(dayName)  // Wednesday

val day = 6
 
when (day) {
    1, 2, 3, 4, 5 -> println("Weekday")
    6, 7 -> println("Weekend")
    else -> println("Invalid")
}

val score = 85
 
when (score) {
    in 90..100 -> println("A")
    in 80..89 -> println("B")
    in 70..79 -> println("C")
    in 50..69 -> println("D")
    else -> println("F")
}

fun describe(obj: Any): String = when (obj) {
    is String -> "String with length ${obj.length}"
    is Int -> "Integer: $obj"
    is Double -> "Double: $obj"
    is Boolean -> "Boolean: $obj"
    else -> "Unknown type"
}
 
println(describe("Hello"))    // String with length 5
println(describe(42))         // Integer: 42
println(describe(3.14))       // Double: 3.14

val age = 25
val hasLicense = true
 
when {
    age < 18 -> println("Too young")
    !hasLicense -> println("No license")
    age >= 18 && hasLicense -> println("Can drive")
    else -> println("Unknown")
}

val score = 95
 
val grade = when (score) {
    in 90..100 -> {
        println("Excellent!")
        "A"  // Giá trị trả về
    }
    in 80..89 -> {
        println("Very good!")
        "B"
    }
    else -> {
        println("Keep trying!")
        "C"
    }
}

enum class Color {
    RED, GREEN, BLUE
}
 
fun getHex(color: Color) = when (color) {
    Color.RED -> "#FF0000"
    Color.GREEN -> "#00FF00"
    Color.BLUE -> "#0000FF"
}

sealed class Result {
    data class Success(val data: String) : Result()
    data class Error(val message: String) : Result()
    object Loading : Result()
}
 
fun handleResult(result: Result) = when (result) {
    is Result.Success -> println("Data: ${result.data}")
    is Result.Error -> println("Error: ${result.message}")
    is Result.Loading -> println("Loading...")
}

// Kotlin when
when (x) {
    1 -> "One"
    2 -> "Two"
    else -> "Other"
}

# Python match (3.10+)
match x:
    case 1:
        "One"
    case 2:
        "Two"
    case _:
        "Other"

fun main() {
    println("""
        === MENU ===
        1. Tạo tài khoản
        2. Đăng nhập
        3. Quên mật khẩu
        4. Thoát
    """.trimIndent())
 
    print("Chọn: ")
    val choice = readln().toIntOrNull() ?: 0
 
    when (choice) {
        1 -> {
            println("Đang tạo tài khoản...")
            createAccount()
        }
        2 -> {
            println("Đang đăng nhập...")
            login()
        }
        3 -> {
            println("Đang reset mật khẩu...")
            resetPassword()
        }
        4 -> println("Tạm biệt!")
        else -> println("Lựa chọn không hợp lệ!")
    }
}
 
fun createAccount() { /* ... */ }
fun login() { /* ... */ }
fun resetPassword() { /* ... */ }