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+---
+language: kotlin
+contributors:
+    - ["S Webber", "https://github.com/s-webber"]
+filename: LearnKotlin.kt
+---
+
+Kotlin is a Statically typed programming language for the JVM, Android and the
+browser. It is 100% interoperable with Java.
+[Read more here.](https://kotlinlang.org/)
+
+```kotlin
+// Single-line comments start with //
+/*
+Multi-line comments look like this.
+*/
+
+// The "package" keyword works in the same way as in Java.
+package com.learnxinyminutes.kotlin
+
+/*
+The entry point to a Kotlin program is a function named "main".
+The function is passed an array containing any command line arguments.
+*/
+fun main(args: Array<String>) {
+    /*
+    Declaring values is done using either "var" or "val".
+    "val" declarations cannot be reassigned, whereas "vars" can.
+    */
+    val fooVal = 10 // we cannot later reassign fooVal to something else
+    var fooVar = 10
+    fooVar = 20 // fooVar can be reassigned
+
+    /*
+    In most cases, Kotlin can determine what the type of a variable is,
+    so we don't have to explicitly specify it every time.
+    We can explicitly declare the type of a variable like so:
+    */
+    val foo : Int = 7
+
+    /*
+    Strings can be represented in a similar way as in Java.
+    Escaping is done with a backslash.
+    */
+    val fooString = "My String Is Here!";
+    val barString = "Printing on a new line?\nNo Problem!";
+    val bazString = "Do you want to add a tab?\tNo Problem!";
+    println(fooString);
+    println(barString);
+    println(bazString);
+
+    /*
+    A raw string is delimited by a triple quote (""").
+    Raw strings can contain newlines and any other characters.
+    */
+    val fooRawString = """
+fun helloWorld(val name : String) {
+   println("Hello, world!")
+}
+"""
+    println(fooRawString)
+
+    /*
+    Strings can contain template expressions.
+    A template expression starts with a dollar sign ($).
+    */
+    val fooTemplateString = "$fooString has ${fooString.length} characters"
+    println(fooTemplateString)
+
+    /*
+    For a variable to hold null it must be explicitly specified as nullable.
+    A variable can be specified as nullable by appending a ? to its type.
+    We can access a nullable variable by using the ?. operator.
+    We can use the ?: operator to specify an alternative value to use
+    if a variable is null
+    */
+    var fooNullable: String? = "abc"
+    println(fooNullable?.length) // => 3
+    println(fooNullable?.length ?: -1) // => 3
+    fooNullable = null
+    println(fooNullable?.length) // => null
+    println(fooNullable?.length ?: -1) // => -1
+
+    /*
+    Functions can be declared using the "fun" keyword.
+    Function arguments are specified in brackets after the function name.
+    Function arguments can optionally have a default value.
+    The function return type, if required, is specified after the arguments.
+    */
+    fun hello(name: String = "world") : String {
+        return "Hello, $name!"
+    }
+    println(hello("foo")) // => Hello, foo!
+    println(hello(name = "bar")) // => Hello, bar!
+    println(hello()) // => Hello, world!
+
+    /*
+    A function parameter may be marked with the "vararg" keyword
+    to allow a variable number of arguments to be passed to the function.
+    */
+    fun varargExample(vararg names: Int) {
+        println("Argument has ${names.size} elements")
+    }
+    varargExample() // => Argument has 0 elements
+    varargExample(1) // => Argument has 1 elements
+    varargExample(1, 2, 3) // => Argument has 3 elements
+
+    /*
+    When a function consists of a single expression then the curly brackets can
+    be omitted. The body is specified after a = symbol.
+    */
+    fun odd(x: Int): Boolean = x % 2 == 1
+    println(odd(6)) // => false
+    println(odd(7)) // => true
+
+    // If the return type can be inferred then we don't need to specify it.
+    fun even(x: Int) = x % 2 == 0
+    println(even(6)) // => true
+    println(even(7)) // => false
+
+    // Functions can take functions as arguments and return functions.
+    fun not(f: (Int) -> Boolean) : (Int) -> Boolean {
+        return {n -> !f.invoke(n)}
+    }
+    // Named functions can be specified as arguments using the :: operator.
+    val notOdd = not(::odd)
+    val notEven = not(::even)
+    // Anonymous functions can be specified as arguments.
+    val notZero = not {n -> n == 0}
+    /*
+    If an anonymous function has only one parameter
+    then its declaration can be omitted (along with the ->).
+    The name of the single parameter will be "it".
+    */
+    val notPositive = not {it > 0}
+    for (i in (0..4)) {
+        println("${notOdd(i)} ${notEven(i)} ${notZero(i)} ${notPositive(i)}")
+    }
+
+    //The "class" keyword is used to declare classes.
+    class ExampleClass(val x: Int) {
+        fun memberFunction(y: Int) : Int {
+            return x + y
+        }
+
+        infix fun infixMemberFunction(y: Int) : Int {
+            return x * y
+        }
+    }
+    /*
+    To create a new instance we call the constructor.
+    Note that Kotlin does not have a "new" keyword.
+    */
+    val fooExampleClass = ExampleClass(7)
+    // Member functions can be called using dot notation.
+    println(fooExampleClass.memberFunction(4)) // => 11
+    /*
+    If a function has been marked with the "infix" keyword then it can be
+    called using infix notation.
+    */
+    println(fooExampleClass infixMemberFunction 4) // => 28
+
+    /*
+    Data classes are a concise way to create classes that just hold data.
+    The "hashCode"/"equals" and "toString" methods are automatically generated.
+    */
+    data class DataClassExample (val x: Int, val y: Int, val z: Int)
+    val fooData = DataClassExample(1, 2, 4)
+    println(fooData) // => DataClassExample(x=1, y=2, z=4)
+
+    // Data classes have a "copy" function.
+    val fooCopy = fooData.copy(y = 100)
+    println(fooCopy) // => DataClassExample(x=1, y=100, z=4)
+
+    // Objects can be destructured into multiple variables.
+    val (a, b, c) = fooCopy
+    println("$a $b $c") // => 1 100 4
+
+    // The "with" function is similar to the JavaScript "with" statement.
+    data class MutableDataClassExample (var x: Int, var y: Int, var z: Int)
+    val fooMutableDate = MutableDataClassExample(7, 4, 9)
+    with (fooMutableDate) {
+        x -= 2
+        y += 2
+        z--
+    }
+    println(fooMutableDate) // => MutableDataClassExample(x=5, y=6, z=8)
+
+    /*
+    We can create a list using the "listOf" function.
+    The list will be immutable - elements cannot be added or removed.
+    */
+    val fooList = listOf("a", "b", "c")
+    println(fooList.size) // => 3
+    println(fooList.first()) // => a
+    println(fooList.last()) // => c
+    // elements can be accessed by index
+    println(fooList[1]) // => b
+
+    // A mutable list can be created using the "mutableListOf" function.
+    val fooMutableList = mutableListOf("a", "b", "c")
+    fooMutableList.add("d")
+    println(fooMutableList.last()) // => d
+    println(fooMutableList.size) // => 4
+
+    // We can create a set using the "setOf" function.
+    val fooSet = setOf("a", "b", "c")
+    println(fooSet.contains("a")) // => true
+    println(fooSet.contains("z")) // => false
+
+    // We can create a map using the "mapOf" function.
+    val fooMap = mapOf("a" to 8, "b" to 7, "c" to 9)
+    // Map values can be accessed by their key.
+    println(fooMap["a"]) // => 8
+
+    // Kotlin provides higher-order functions for working with collections.
+    val x = (1..9).map {it * 3}
+                  .filter {it < 20}
+                  .groupBy {it % 2 == 0}
+                  .mapKeys {if (it.key) "even" else "odd"}
+    println(x) // => {odd=[3, 9, 15], even=[6, 12, 18]}
+
+    // A "for" loop can be used with anything that provides an iterator.
+    for (c in "hello") {
+        println(c)
+    }
+
+    // "while" loops work in the same way as other languages.
+    var ctr = 0
+    while (ctr < 5) {
+        println(ctr)
+        ctr++
+    }
+    do {
+        println(ctr)
+        ctr++
+    } while (ctr < 10)
+
+    // "when" can be used as an alternative to "if-else if" chains.
+    val i = 10
+    when {
+        i < 7 -> println("first block")
+        fooString.startsWith("hello") -> println("second block")
+        else -> println("else block")
+    }
+
+    // "when" can be used with an argument.
+    when (i) {
+        0, 21 -> println("0 or 21")
+        in 1..20 -> println("in the range 1 to 20")
+        else -> println("none of the above")
+    }
+
+    // "when" can be used as a function that returns a value.
+    var result = when (i) {
+        0, 21 -> "0 or 21"
+        in 1..20 -> "in the range 1 to 20"
+        else -> "none of the above"
+    }
+    println(result)
+
+    /*
+    We can check if an object is a particular type by using the "is" operator.
+    If an object passes a type check then it can be used as that type without
+    explicitly casting it.
+    */
+    fun smartCastExample(x: Any) : Boolean {
+        if (x is Boolean) {
+            // x is automatically cast to Boolean
+            return x
+        } else if (x is Int) {
+            // x is automatically cast to Int
+            return x > 0
+        } else if (x is String) {
+            // x is automatically cast to String
+            return x.isNotEmpty()
+        } else {
+            return false
+        }
+    }
+    println(smartCastExample("Hello, world!")) // => true
+    println(smartCastExample("")) // => false
+    println(smartCastExample(5)) // => true
+    println(smartCastExample(0)) // => false
+    println(smartCastExample(true)) // => true
+
+    /*
+    Extensions are a way to add new functionality to a class.
+    This is similar to C# extension methods.
+    */
+    fun String.remove(c: Char): String {
+        return this.filter {it != c}
+    }
+    println("Hello, world!".remove('l')) // => Heo, word!
+
+    println(EnumExample.A) // => A
+    println(ObjectExample.hello()) // => hello
+}
+
+// Enum classes are similar to Java enum types.
+enum class EnumExample {
+    A, B, C
+}
+
+/*
+The "object" keyword can be used to create singleton objects.
+We cannot assign it to a variable, but we can refer to it by its name.
+This is similar to Scala singleton objects.
+*/
+object ObjectExample {
+    fun hello() : String {
+        return "hello"
+    }
+}
+
+```
+
+### Further Reading
+
+A web-based mini-IDE for Kotlin:
+[http://try.kotlinlang.org/)