Learn Kotlin by Example

Introduction

Functions

fun aFunction(arg1: Arg1Type, optionalArg: OptionalArgType = defaultVal): ReturnType {
// ...
}

fun printStuff(stuff: String, prefix: String = "Info") {
    print("[$prefix] $stuff")
}

fun main() {
    // Many valid ways to call printStuff
    print("thing")
    print("thing", "hello")
    print(stuff = "thing", prefix = "hello")
    print(prefix = "hello", stuff = "thing")
}
 ```

 ## [Infix Functions](https://kotlinlang.org/docs/functions.html#infix-notation): `infix`
 Member and extension functions with a single parameter can be turned into `infix` functions (calling it doesn't require a dot or parentheses)
 > Almost in a way making your own keywords? Probably how Boolean or is just '`or`'
```kotlin
infix fun Int.times(str: String) = str.repeat(this)
println(2 times "Bye ")

Bye Bye

Operator Overloading

In an addition to infix functions, using the operator keyword with some special names will overload an operator symbol

operator fun Vector.plus(v2: Vector) = Vector(this.x + v2.x, this.y + v2.y)
println(aVector + anotherVector)

Varargs

A funky kind of inline array? Come back to this.

The mechanism by which listOf() works, I think

Class Declarations

In Kotlin, both the header and the body are optional, since the compiler can build the constructor and appropriate getters/setters for you

// All valid class declarations

class Customer
// a default constructor is inferred

class Contact(val id: Int, var email: String)
// builds a constructor

fun main() {
    val contact = Contact(1, "[email protected]")
    println(contact.email)
    contact.email = "[email protected]"
    println(contact.email)
}

[email protected] [email protected]

Note: `new` keyword doesn't exist in Kotlin

Inheritance

Classes and functions are final by default in Kotlin. If you want one to be able to be overriden, mark it with the open keyword.

open class Dog {
    open fun sayHello() {
        println("woof")
    }
}

class Yorkshire : Dog() {
    override fun sayHello() {
        println("yip")
    }
}

fun main() {
    val dog: Dog = Yorkshire()
}

Control Flow

To be continued...