Chuyển đổi kiểu dữ liệu (Type Conversion) trong Kotlin

val int: Int = 10
val long: Long = 20L
 
// val sum = int + long  // ERROR: Type mismatch!
 
// Phải chuyển đổi tường minh
val sum1 = int.toLong() + long     // OK
val sum2 = int + long.toInt()      // OK

val num = 100
 
val byte = num.toByte()
val short = num.toShort()
val int = num.toInt()
val long = num.toLong()
val float = num.toFloat()
val double = num.toDouble()
val char = num.toChar()  // ASCII code

val number = 42
 
val str1 = number.toString()
val str2 = "$number"  // String template
val str3 = number.toString(2)   // Binary: "101010"
val str4 = number.toString(16)  // Hex: "2a"

val str = "123"
 
// Unsafe conversion (throws exception if invalid)
val int = str.toInt()
val double = str.toDouble()
val long = str.toLong()
 
// Safe conversion (returns null if invalid)
val safeInt = str.toIntOrNull()
val safeDouble = str.toDoubleOrNull()
 
if (safeInt != null) {
    println("Valid number: $safeInt")
} else {
    println("Invalid number")
}
 
// With default value
val value = str.toIntOrNull() ?: 0

val char = 'A'
 
val code = char.code           // 65 (ASCII)
val digit = '5'.digitToInt()  // 5
 
val charFromCode = 65.toChar()  // 'A'

val bool = true
 
val str = bool.toString()  // "true"
 
// String to Boolean
val b1 = "true".toBoolean()   // true
val b2 = "false".toBoolean()  // false
val b3 = "yes".toBoolean()    // false (chỉ nhận "true")

val obj: Any = "Hello"
 
// Unsafe cast
val str: String = obj as String  // OK
 
// Safe cast (returns null if fails)
val num: Int? = obj as? Int      // null (không throw exception)

fun printLength(obj: Any) {
    if (obj is String) {
        // obj tự động được cast thành String
        println(obj.length)  // OK, không cần cast
    }
}
 
// With when
fun describe(obj: Any): String = when (obj) {
    is String -> "String of length ${obj.length}"
    is Int -> "Integer: $obj"
    is Double -> "Double: $obj"
    else -> "Unknown"
}

fun getUserAge(): Int {
    while (true) {
        print("Enter your age: ")
        val input = readln()
        val age = input.toIntOrNull()
 
        if (age != null && age in 0..150) {
            return age
        } else {
            println("Invalid age. Please try again.")
        }
    }
}
 
fun parseDouble(str: String, default: Double = 0.0): Double {
    return str.toDoubleOrNull() ?: default
}

val list = listOf(1, 2, 3, 4, 5)
 
val array = list.toTypedArray()
val set = list.toSet()
val mutableList = list.toMutableList()
 
// Convert types
val doubles = list.map { it.toDouble() }  // [1.0, 2.0, 3.0, 4.0, 5.0]
val strings = list.map { it.toString() }  // ["1", "2", "3", "4", "5"]