Kotlin General Notes

Random Links

• https://www.baeldung.com/kotlin/multiplatform-programming

Compose Desktop/Mobile UI Skia

• https://skia.org/
• https://developer.android.com/jetpack/compose
• https://www.jetbrains.com/lp/compose/
• https://github.com/JetBrains/compose-jb/blob/master/tutorials/Getting_Started/README.md
• https://github.com/JetBrains/compose-jb/tree/master/examples/imageviewer
• https://github.com/JetBrains/compose-jb/tree/master/examples/issues

Types =====

• Reference: https://kotlinlang.org/docs/reference/basic-types.html

Numbers

• Byte: 8, -128..128
• Short: 32768 .. 32767
• Int: -2,147,483,648 (-231) .. 2,147,483,647 (231 - 1)
• Long: -9,223,372,036,854,775,808 (-263) .. 9,223,372,036,854,775,807 (263 - 1)
• Float: size 32
• Double: size 64

//
val one = 1 // Int
val threeBillion = 3000000000 // Long
val oneLong = 1L // Long
val oneByte: Byte = 1

//
val pi = 3.14 // Double
val e = 2.7182818284 // Double
val eFloat = 2.7182818284f // Float, actual value is 2.7182817

//
fun main() {
    fun printDouble(d: Double) { print(d) }

    val i = 1
    val d = 1.1
    val f = 1.1f

    printDouble(d)
    //    printDouble(i) // Error: Type mismatch
    //    printDouble(f) // Error: Type mismatch
}


// Underscores in numeric literals
val oneMillion = 1_000_000
val creditCardNumber = 1234_5678_9012_3456L
val socialSecurityNumber = 999_99_9999L
val hexBytes = 0xFF_EC_DE_5E
val bytes = 0b11010010_01101001_10010100_10010010

// Hypothetical code, does not actually compile:
val a: Int? = 1 // A boxed Int (java.lang.Integer)
val b: Long? = a // implicit conversion yields a boxed Long (java.lang.Long)
print(b == a) // Surprise! This prints "false" as Long's equals() checks whether the other is Long as well

Literal constants

• Decimals: 123, Longs tagged with L
• Hexadecimals: Ox0F
• Binaries: 0b000001011
• Octal: Not supported
• Doubles by default: 123.5, 123.5e10

Explicit conversions

• toByte():Byte
• toInt():Int
• toLong():Long
• toFloat:Float
• toDouble:Double
• toChar():Char

    val l = 1L + 3 // Long + Int => Long

Characters

• Char cannot be treated as a number.
• Character literals go in single quotes: ‘1’
• Supported escape sequences: \t, \b, \n, \r, \', \", \\ and \$

fun check(c: Char) {
    if (c == 1) { // ERROR: incompatible types
        // ...
    }
}

Booleans

• two values: true and false
• || – lazy disjunction
• && – lazy conjunction
• ! - negation

Array

• Array has get/set access that is implemented by []
• Array has size for length.