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"source": "* Official list of idioms: https://kotlinlang.org/docs/idioms.html\n",
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"## Preamble/Important notes\n",
"\n",
"* \"Syntactic sugar\" is a false concept. Each language feature affects how we use the language.\n",
"* One can adopt different programming styles in Kotlin. Idiomatic kotlin is an unofficial combination of practices developed by experienced Kotlin users.\n",
"* One of the key features of idiomatic kotlin is to use scopes instead of objects to provide incapsulation and limit visible mutable state.\n",
"\n",
"### What is idiomatic Kotlin (roughly)?\n",
"\n",
"* Less \"ceremony\". Pragmatic approach.\n",
"* Hybrid object/functional paradigm (objects for data, functions for interactions).\n",
"* Don't use mutable state wherever read-only is enough.\n",
"* Don't use classes when functions are enough.\n",
"* Don't use inheritance when composition is enough.\n",
"* Function is a first-class citizen.\n",
"* Scope is a first-class citizen.\n",
"* Use extensions to separate inner workings from utilities.\n",
"\n",
"### Do not do\n",
"\n",
"* Scope pollution.\n",
"* Scope function abuse.\n",
"* Rely on initialization order."
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"source": [
"## String interpolation\n",
"\n",
"Interpolated string allows constructing string fast"
],
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"cell_type": "code",
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"source": "println(\"This is a plain string\")",
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"source": [
"val arg = \"Interpolated\"\n",
"println(\"This is an $arg string\")"
],
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"cell_type": "code",
"source": [
"val number = 1\n",
"\n",
"fun increment(num: Int) = num + 1\n",
"println(\"This is an $arg string number ${increment(number) + 1}\")"
],
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"cell_type": "code",
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"source": "println(\"This is a string with \\$\")",
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"cell_type": "code",
"source": [
"println(\"\"\"\n",
" This is a \n",
" multi\n",
" line\n",
" raw\n",
" string\n",
"\"\"\".trimIndent())"
],
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"cell_type": "code",
"source": [
"println(\"\"\"This is a raw string number ${number+1} with \\ and ${'$'} \"\"\")"
],
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"source": [
"## Make `val`, not `var`!\n",
"\n",
"`val` means read-only property\n",
"\n",
"`var` means writable property\n",
"\n",
"Unnecessary use of `var` is not recommended.\n",
"\n",
"**NOTE:** In performance critical cases, explicit cycles are better, but mutable state should be encapsulated."
],
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"cell_type": "code",
"source": [
"/* Not recommended */\n",
"var counter = 0\n",
"for(i in 0..20){\n",
" counter += i\n",
"}\n",
"counter"
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"cell_type": "code",
"source": [
"/* recommended */\n",
"val sum = (0..20).sum()\n",
"sum"
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"cell_type": "code",
"source": [
"val intArray: IntArray = IntArray(21){ it -> it + 1 }\n",
"intArray.sum()"
],
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"source": [
"## Top level functions\n",
"\n",
"Don't create a class when a function is enough.\n",
"\n",
"Use access modifiers for incapsulation."
],
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"source": [
"/**\n",
" * Functions could be defined everywhere in kotlin code. This is a so-called top-level function.\n",
" */\n",
"fun doSomething(){\n",
" println(\"I did it\")\n",
"}\n",
"\n",
"doSomething()"
],
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"source": [
"interface AnInterface{\n",
" fun doSomethingInAnObject()\n",
"}\n",
"\n",
"object AnObject : AnInterface{\n",
" /**\n",
" * This is a member-function\n",
" */\n",
" override fun doSomethingInAnObject(){\n",
" println(\"I did it in an object\")\n",
" }\n",
"}\n",
"\n",
"AnObject.doSomethingInAnObject()"
],
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"cell_type": "code",
"source": [
"fun doSomethingSpecial(){\n",
" val base = \"base\"\n",
" val special = \"special\"\n",
" /**\n",
" * This one is inside another function\n",
" */\n",
" fun String.doSomethingInside(){\n",
" println(\"I did $special inside another function on $this\")\n",
" }\n",
" base.doSomethingInside()\n",
"}\n",
"//\"ddd\".doSomethingInside()\n",
"\n",
"doSomethingSpecial()"
],
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"source": [
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"fun returnFunction(): (String) -> Unit {\n",
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" fun printStringWithPrefix(str: String){\n",
" println(\"Prefixed: $str\")\n",
" }\n",
" return ::printStringWithPrefix\n",
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" //return { printStringWithPrefix(it) }\n",
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" // return { println(\"Prefixed: $it\") }\n",
"}\n",
"\n",
"returnFunction()(\"Haskel, Boo!\")"
],
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"cell_type": "markdown",
"source": [
"## Unit"
],
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"\n",
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"fun returnUnit(): Unit {\n",
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" // no return statement `Unit` is returned implicitly\n",
" val b = Unit\n",
"}"
],
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"metadata": {},
"cell_type": "code",
"source": [
"fun doNothing(){\n",
" \n",
"}\n",
"\n",
"val a = doNothing()\n",
"a::class"
],
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"cell_type": "markdown",
"source": [
"## Default parameters"
],
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"cell_type": "code",
"source": [
"fun doSomethingWithDefault(a: Int = 0, b: String = \"\") {\n",
" println(\"A string with a == $a and b == \\\"$b\\\"\")\n",
"}\n",
"\n",
"doSomethingWithDefault()\n",
"doSomethingWithDefault(2, \"aaa\")\n",
"doSomethingWithDefault(b = \"fff\", a = 8)\n",
"doSomethingWithDefault(4, b = \"fff\")\n",
"doSomethingWithDefault(a = 2, \"fff\")// don't do that"
],
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"cell_type": "code",
"source": [
"fun integrate(\n",
" from: Double = 0.0,\n",
" to: Double = 1.0,\n",
" step: Double = 0.01,\n",
" function: (Double) -> Double,\n",
"): Double {\n",
" require(to > from)\n",
" require(step > 0)\n",
" var sum = 0.0\n",
" var pos = from\n",
" while (pos < to) {\n",
" sum += function(pos)\n",
" pos += step\n",
" }\n",
" return sum*step\n",
"}\n",
"\n",
"integrate { x ->\n",
" x * x + 2 * x + 1\n",
"}\n",
"integrate(0.0, PI) { sin(it) }\n",
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"// integrate(0.0, PI) //error\n",
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"integrate(0.0, step = 0.02, to = PI) { sin(it) }\n",
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"//integrate(0.0, step = 0.02, PI) { sin(it) }\n",
"\n",
"integrate(0.0, step = 0.02, function = { sin(it) }, to = PI)"
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"cell_type": "code",
"source": [
"fun functionWithParameters(){\n",
" println(\"without default\")\n",
"}\n",
"\n",
"//@JvmOverloads\n",
"@JvmName(\"functionWithDefaultParameters\")\n",
"fun functionWithParameters(a: Int = 2){\n",
" println(\"with default\")\n",
"}\n",
"\n",
"functionWithParameters()"
],
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"cell_type": "markdown",
"source": [
"## Function body shortcut"
],
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"cell_type": "code",
"source": [
"fun theSameAsBefore(a: Int = 0, b: String = \"\"): String = \"A string with a == $a and b == $b\"\n",
"\n",
"class Context(val a: String, val b: String)\n",
"\n",
"fun somethingWith(context: Context) = with(context){\n",
" println(a + b)\n",
"}"
],
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"cell_type": "markdown",
"source": [
"## Trailing lambda\n",
"\n",
"Scope is a separate important concept in Kotlin"
],
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"source": [
"data class BuildResult internal constructor(val str: String, val int: Int, val optional: Double?){\n",
" init{\n",
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" require(optional!= null){ \"null!\" }\n",
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" }\n",
"}\n",
"\n",
"class Builder(\n",
" var str: String = \"\", \n",
" var int: Int = 0\n",
"){\n",
" var optional: Double? = null\n",
"\n",
" fun build() = BuildResult(str, int, optional)\n",
"}\n",
"\n",
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"fun BuildResult(defaultInt: Int, block: Builder.() -> Unit): BuildResult = \n",
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" Builder(int = defaultInt).apply(block).build()\n",
"\n",
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"val res = BuildResult(2){\n",
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" str = \"ff\"\n",
" optional = 1.0\n",
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"}\n",
"\n",
"res"
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"cell_type": "markdown",
"source": [
"## Inheritance"
],
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"source": [
"//Interfaces and objects\n",
"\n",
"interface AnInterface {\n",
" val a: Int\n",
" get() = 4\n",
" // set(value){\n",
" // println(value)\n",
" // }\n",
" fun doSomething() //= println(\"From interface\")\n",
"}\n",
"\n",
"abstract class AnAbstractClass(override val a: Int): AnInterface{\n",
" override final fun doSomething() = println(\"From a class\")\n",
" abstract fun doSomethingElse()\n",
"}\n",
"\n",
"class AClass(override val a: Int) : AnInterface {\n",
" override fun doSomething() = println(\"From a class\")\n",
"}\n",
"\n",
"class BClass(a: Int) : AnAbstractClass(a) {\n",
" override fun doSomethingElse() = println(\"something else\")\n",
"}\n",
"\n",
"/**\n",
" * A singleton (object) is a type (class) which have only one instance\n",
" */\n",
"object AnObject : AnInterface {\n",
" override fun doSomething(): Unit = TODO(\"Not yet implemented\")\n",
"}\n",
"\n",
"/**\n",
"* Creating an instance\n",
"*/\n",
"val instance = AClass(3)\n",
"\n",
"/**\n",
"* Using singleton reference without constructor invocation\n",
"*/\n",
"val obj: AnInterface = AnObject\n",
"\n",
"/**\n",
"* Anonymous object\n",
"*/\n",
"val anonymous = object : AnInterface {\n",
" override fun doSomething(): Unit = TODO(\"Not yet implemented\")\n",
"}\n",
"\n",
"/**\n",
"* The one that should not be named\n",
"*/\n",
"val voldemort = object {\n",
" fun doSomething(): Unit = TODO()\n",
"}\n",
"\n",
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"// voldemort.doSomething()"
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"source": [
"fun interface Float64Function: (Double) -> Double {\n",
" override operator fun invoke(arg: Double): Double\n",
" \n",
" operator fun invoke(doubles: DoubleArray): DoubleArray = DoubleArray(doubles.size){ invoke( doubles[it]) }\n",
"}\n",
"\n",
"val sin = object : Float64Function{\n",
" override fun invoke(p1: Double): Double = sin(p1)\n",
"}\n",
"\n",
"val cos = Float64Function{ kotlin.math.cos(it) }\n",
"\n",
"val tg = Float64Function(::tan)\n",
"\n",
"sin(PI/2)\n",
"\n",
"sin(doubleArrayOf(0.0, PI/2))"
],
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"cell_type": "markdown",
"source": [
"## Declaration site variance\n",
"\n",
"In consumes, out produces."
],
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"cell_type": "code",
"source": [
"interface Producer<out T>{\n",
" fun produce(): T\n",
"}\n",
"\n",
"interface Consumer<in T>{\n",
" fun consume(value: T)\n",
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"}\n",
"\n",
"interface Doer<T>: Producer<T>, Consumer<T> {\n",
"\n",
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"}"
],
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"outputs": [],
"execution_count": null
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{
"cell_type": "markdown",
"source": [
"## Return on when\n",
"https://kotlinlang.org/docs/idioms.html#return-on-when-statement"
],
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"cell_type": "code",
"source": [
"fun transform(color: String): Int = when (color) {\n",
" \"Red\" -> 0\n",
" \"Green\" -> 1\n",
" \"Blue\" -> 2\n",
" else -> throw IllegalArgumentException(\"Invalid color param value\")\n",
"}"
],
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"hide_output_from_viewers": true
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2024-11-12 09:20:43 +03:00
{
"metadata": {},
"cell_type": "code",
"source": "fun transformIf(flag: Boolean): Int = if (flag) 1 else 0 ",
"outputs": [],
"execution_count": null
},
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{
"cell_type": "markdown",
"source": [
"## Runtime type dispatch\n",
"\n",
"In Java it is called DOP (Data Oriented Programming).\n",
"\n",
"Also, sometimes (wrongly) called pattern matching."
],
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"cell_type": "code",
"source": [
"/**\n",
" * Matching by type\n",
" */\n",
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"fun checkType(arg: Any): Unit = when (arg) {\n",
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" is String -> println(\"I am a String. Length is ${arg.length}\")\n",
" is Int -> println(\"I am an Int.\")\n",
" is Double -> println(\"I am a Double\")\n",
" // 2==2 -> println(\"Wat?\")\n",
" else -> println(\"I don't know who am I?\")\n",
"}\n",
"\n",
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"fun checkType2(arg: Any): Unit = when {\n",
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" arg is String -> println(\"I am a String\")\n",
" arg is Int -> println(\"I am an Int\")\n",
" arg is Double -> println(\"I am a Double\")\n",
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" 2 == 2 -> println(\"Wat?\")\n",
2024-10-29 09:30:55 +03:00
" else -> println(\"I don't know who am I?\")\n",
"}\n",
"\n",
"checkType(true)"
],
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"cell_type": "markdown",
"source": [
"## Try-catch expression\n",
"https://kotlinlang.org/docs/idioms.html#try-catch-expression"
],
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"cell_type": "code",
"source": [
"fun tryCatch() {\n",
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" val result: Int = try {\n",
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" 22\n",
" } catch (e: ArithmeticException) {\n",
" throw IllegalStateException(e)\n",
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" } finally {\n",
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" println(\"finally\")\n",
" }\n",
"\n",
" // Working with result\n",
"}"
],
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"cell_type": "code",
"source": [
"\n",
"val res: Result<Int> = runCatching<Int> { \n",
" //error(\"Error happened\")\n",
" 4\n",
"}\n",
"\n",
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"println(res.exceptionOrNull())\n",
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"(res.getOrNull() ?: 0) + 1"
],
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"node_id": "MslvYANHimu0ByBevtI4NY",
"type": "CODE",
"hide_input_from_viewers": true,
"hide_output_from_viewers": true
}
},
"outputs": [],
"execution_count": null
},
{
"cell_type": "code",
"source": [
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"val dataFlow = sequence {\n",
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" var i = 0\n",
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" while (true) {\n",
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" yield(i++)\n",
" }\n",
"}\n",
"\n",
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"dataFlow.map {\n",
" runCatching {\n",
" if (it % 2 == 0) error(\"Even: $it\") else it\n",
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" }\n",
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"}.take(10).toList().joinToString(separator = \"\\n\")"
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],
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"hide_output_from_viewers": true
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"execution_count": null
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{
"cell_type": "markdown",
"source": [
"## Nothing"
],
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"cell_type": "code",
"source": [
"/**\n",
" * The declaration if valid because [TODO] returns Nothing\n",
" */\n",
"fun getSomething(): Int? = TODO()\n",
"\n",
"fun findSomething(): Int {\n",
" // early return is valid because `return` operator result is Nothing\n",
" val found: Int = getSomething() ?: return 2\n",
" return found + 2\n",
"}\n",
"\n",
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"//FIXME don't do that\n",
"fun dontDoThat() {\n",
" if (true) return\n",
" println(false)\n",
"}\n",
"\n",
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"fun checkCondition(): Int {\n",
" fun conditionSatisfied() = false\n",
"\n",
" return if (conditionSatisfied()) {\n",
" 1\n",
" } else {\n",
" //error is Nothing\n",
" error(\"Condition is not satisfied\")\n",
" }\n",
"}"
],
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"cell_type": "markdown",
"source": [
"## Data class"
],
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"source": [
"\n",
"class SimpleClass(val a: Int, val b: Double, c: Double){\n",
" override fun toString() = \"SimpleClass(a=$a, b=$b)\"\n",
"}\n",
"\n",
"\n",
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"data class DataClass(val a: Int, var b: Double /*, d: Double */) {\n",
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" val c get() = b + 1\n",
"}\n",
"\n",
"val simple = SimpleClass(1, 2.0, 3.0)\n",
"\n",
"println(simple)\n",
"\n",
"val data = DataClass(2, 2.0)\n",
"val copy = data.copy(b = 22.2)\n",
"println(copy)"
],
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"cell_type": "markdown",
"source": [
"## Nullable truth"
],
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"cell_type": "code",
"source": [
"/**\n",
" * Nullable truth.\n",
" */\n",
"fun nullableTruth() {\n",
" class A(val b: Boolean?)\n",
"\n",
" val a: A? = A(null) // Compilator warning here\n",
" //use\n",
" a?.b == true\n",
" //instead of\n",
" a?.b ?: false\n",
"\n",
" // The old way\n",
" val res = if (a == null) {\n",
" false\n",
" } else {\n",
" if (a.b == null) {\n",
" false\n",
" } else {\n",
" a.b\n",
" }\n",
" }\n",
"}"
],
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"node_id": "5BN3u1gHkSamtLIJiQicsV",
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"hide_output_from_viewers": true
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},
"outputs": [],
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{
"metadata": {},
"cell_type": "code",
"source": [
"import java.util.Optional\n",
"import kotlin.reflect.typeOf\n",
"\n",
"println(typeOf<Optional<Boolean>>() == typeOf<Optional<Optional<Boolean>>>())\n",
"\n",
"println( typeOf<Boolean?>() == typeOf<Boolean??>()) "
],
"outputs": [],
"execution_count": null
},
{
"metadata": {},
"cell_type": "code",
"source": "mapOf<String,String>().get(\"f\")!!",
"outputs": [],
"execution_count": null
},
2024-10-29 09:30:55 +03:00
{
"cell_type": "markdown",
"source": [
"## Safe call"
],
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"source": [
"\n",
"/**\n",
" * Safe call and elvis operator\n",
" */\n",
"fun idiom12() {\n",
" val files = File(\"Test\").listFiles()\n",
" println(files?.size ?: \"empty\")\n",
"}\n",
"idiom12()"
],
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"cell_type": "code",
"source": [
"fun printNotNull(any: Any) = println(any)\n",
"\n",
"// printNotNull(null) does not work\n",
"\n",
"val value: Int? = 2\n",
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"//val value: Int? by lazy { 2 }\n",
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"\n",
"//printNotNull(value) // Error\n",
"if (value != null) {\n",
" //not guaranteed to work with mutable variable\n",
" printNotNull(value)\n",
"}\n",
"\n",
"var value1: Int? = 2\n",
"\n",
"// Safe call here\n",
"value1?.let {\n",
" printNotNull(it) // execute this block if not null\n",
" //printNotNull(value1) // value is not null here\n",
"}"
],
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"cell_type": "markdown",
"source": [
"## Nullable assignment"
],
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"cell_type": "code",
"source": [
"\n",
"/**\n",
" * Dart-like (?=) nullable assignment\n",
" */\n",
"fun idiom11() {\n",
" var x: String? = null\n",
" x = x ?: \"Hello\"\n",
"}"
],
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"node_id": "di2EXkn35CFEja9KMK1Ur5",
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"hide_output_from_viewers": true
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"cell_type": "markdown",
"source": [
"## Extension functions"
],
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"cell_type": "code",
"source": [
"/**\n",
" * Extension function on a String. It is not monkey-patching.\n",
" */\n",
"fun String.countOs(): Int = count { it == 'ы' } // implicit this points to String\n",
"\n",
"fun Int.printMe() = println(this) // explicit this\n",
"\n",
"fun Any?.doSomething(): Int = TODO(\"Don't do that\")\n",
"\n",
"fun ((Int) -> Int).evalAndIncrement(): (Int) -> Int = { this.invoke(it) + 1 }\n",
"\n",
"// val intFunction: (Int)->Int = {it -1}\n",
"\n",
"// val modifiedFunction = intFunction.evalAndIncrement()\n",
"\n",
"// println(modifiedFunction(0))\n",
"\n",
"\"вылысыпыдыстычка\".countOs().printMe()"
],
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"node_id": "li65OumXRClbEIwURW9DEE",
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"cell_type": "code",
"source": [
"infix fun <T: Comparable<T>> ClosedRange<T>.intersect(other: ClosedRange<T>): ClosedRange<T>?{\n",
" val start = maxOf(this.start, other.start)\n",
" val end = minOf(this.endInclusive, other.endInclusive)\n",
" return if(end>=start) start..end else null\n",
"}\n",
"\n",
"(0..8).intersect(6..12)\n",
"0..8 intersect 6..12"
],
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"hide_output_from_viewers": true
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2024-11-12 09:20:43 +03:00
{
"metadata": {},
"cell_type": "code",
"source": "",
"outputs": [],
"execution_count": null
},
2024-10-29 09:30:55 +03:00
{
"cell_type": "code",
"source": [
"fun List<String>.concat() = joinToString(separator = \"\")\n",
"listOf(\"a\",\"b\",\"c\").concat()\n",
"listOf(1,2,3).concat()"
],
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"datalore": {
"node_id": "tnCskYd7474gKZiYnPHlx4",
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"hide_output_from_viewers": true
}
},
"outputs": [],
"execution_count": null
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2024-11-12 09:20:43 +03:00
{
"metadata": {},
"cell_type": "code",
"source": "",
"outputs": [],
"execution_count": null
},
{
"metadata": {},
"cell_type": "code",
"source": [
"val functionWithReciever: List<String>.(arg: Int) -> Unit = {arg->\n",
" println(get(arg))\n",
"}\n",
"\n",
"listOf(\"1\", \"2\", \"3\").functionWithReciever(1)"
],
"outputs": [],
"execution_count": null
},
2024-10-29 09:30:55 +03:00
{
"cell_type": "markdown",
"source": [
"## Extension properties\n",
"\n",
"Remember [property usage guidelines](https://kotlinlang.org/docs/coding-conventions.html#functions-vs-properties)."
],
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"source": [
"\n",
"/**\n",
" * Extension property (must be virtual)\n",
" */\n",
"val List<Number>.odd get() = filter { it.toInt() % 2 == 1 }\n",
"\n",
"List(10){it}.odd"
],
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"hide_output_from_viewers": true
}
},
"outputs": [],
"execution_count": null
},
{
"cell_type": "code",
"source": [
"var MutableMap<String, String>.a: String?\n",
" get() = this.get(\"a\")\n",
" set(value){\n",
" if(value == null){\n",
" this.remove(\"a\")\n",
" } else {\n",
" this.set(\"a\",value)\n",
" }\n",
" }\n",
"\n",
"val map = mutableMapOf(\"a\" to \"a\", \"b\" to \"b\")\n",
"\n",
"map.a = \"6\"\n",
"\n",
"map.a"
],
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"node_id": "9DG1gyyYvzjbg0EZFfP5Qo",
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"hide_output_from_viewers": true
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"cell_type": "code",
"source": [
"\n",
"/**\n",
" * Extension variable (also must be virtual)\n",
" */\n",
"var Array<Int>.second: Int\n",
" get() = this[1]\n",
" set(value) {\n",
" this[1] = value\n",
" }\n",
"\n",
"\n",
"val array = Array(5){it}\n",
"array.second = 9\n",
"array"
],
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"hide_output_from_viewers": true
}
},
"outputs": [],
"execution_count": null
},
{
"cell_type": "markdown",
"source": [
"## Scope functions (run, with, let)"
],
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"cell_type": "code",
"source": [
"object AClass{\n",
" val a = \"a\"\n",
" val b = \"b\"\n",
" val c = \"c\"\n",
"}\n",
"\n",
"fun getAClass(): AClass? = null\n",
"\n",
"/**\n",
" * [with]/[run]/[let] are used to create a scope with given argument or receiver\n",
" */\n",
"\n",
"\n",
"// Simple print of AClass\n",
"println(\"a = ${AClass.a}, b = ${AClass.b}, c = ${AClass.c}\")\n",
"\n",
"// Using `with`\n",
"val res = with(AClass){\n",
" // AClass type is the receiver in this scope\n",
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" println(\"a = ${this.a}, b = $b, c = $c\")\n",
2024-10-29 09:30:55 +03:00
" /*return@with*/ \"some value\"\n",
"}\n",
"\n",
"res"
],
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"hide_output_from_viewers": true
}
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2024-11-12 09:20:43 +03:00
{
"metadata": {},
"cell_type": "code",
"source": [
"object AContext{\n",
" fun AClass.abc() = a + b + c // warning additional concatenation\n",
"}\n",
"\n",
"fun printAbc(aClass: AClass) = with(AContext){\n",
" aClass.abc()\n",
"}"
],
"outputs": [],
"execution_count": null
},
2024-10-29 09:30:55 +03:00
{
"cell_type": "code",
"source": [
"\n",
"//using `run`\n",
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"getAClass()?.takeIf { it.a.isNotEmpty() }?.run {\n",
2024-10-29 09:30:55 +03:00
" // the same as above\n",
" println(\"a = $a, b= $b, c = $c\")\n",
" 2\n",
"}\n",
"\n",
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"val runResult: Int = run {\n",
" \n",
"}\n",
"\n",
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"//Using `let` to compose result. Not recommended using without a need\n",
"val letResult = getAClass()?.let { arg ->\n",
" arg.c + arg.a\n",
"}\n"
],
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"hide_output_from_viewers": true
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"outputs": [],
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{
"metadata": {},
"cell_type": "code",
"source": [
"//Don't do that\n",
"fun scopeAbuse(str: String?) = str.takeIf { it?.isNotEmpty() == true }?.let { it.substring(0..4) }?.let { it.matches(\".*\".toRegex())}"
],
"outputs": [],
"execution_count": null
},
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{
"cell_type": "markdown",
"source": [
"## Scope functions (also, apply)"
],
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"cell_type": "code",
"source": [
"/**\n",
" * Using apply/also to add a finalizing action\n",
" */\n",
"var i = 2\n",
"\n",
"/**\n",
"* [also] block does not affect the result\n",
"*/\n",
"fun getAndIncrement() = i.also { i += 1 } //don't do that\n",
"\n",
"println(getAndIncrement())\n",
"println(i)"
],
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"hide_output_from_viewers": true
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"outputs": [],
"execution_count": null
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{
"cell_type": "code",
"source": [
"\n",
"class Rectangle {\n",
" var length: Number = 0\n",
" var breadth: Number = 0\n",
" var color: Int = 0xffffff\n",
"}\n",
"\n",
"/**\n",
" * Configure properties of an object (apply)\n",
" * https://kotlinlang.org/docs/idioms.html#configure-properties-of-an-object-apply\n",
" */\n",
"val myRectangle = Rectangle().apply {\n",
" length = 4\n",
" breadth = 5\n",
" color = 0xFAFAFA\n",
"}\n",
"\n",
"fun Rectangle(block: Rectangle.() -> Unit): Rectangle = Rectangle().apply(block)\n",
"\n",
"val myRectangle2 = Rectangle {\n",
" length = 4\n",
" breadth = 5\n",
" color = 0xFAFAFA\n",
"}\n",
"\n",
"fun Rectangle(length: Number) = Rectangle().apply { this.length = length }\n",
"\n",
"Rectangle(8)"
],
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"outputs": [],
"execution_count": null
},
{
"cell_type": "markdown",
"source": [
"## Lists\n",
"\n",
"Do not cast List to MutableList!"
],
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"cell_type": "code",
"source": [
"/**\n",
" * Lists and mutable lists\n",
" */\n",
"\n",
"\n",
"/**\n",
" * This method creates a read-only list of strings. One should note that the type of the list is not specified\n",
" */\n",
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"val list: List<String> = listOf(\"a\", \"b\", \"c\")\n",
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"\n",
"println(list[0])\n",
"println(list.get(1))\n",
"//println(list.get(4))\n",
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"println(list.getOrNull(4) ?: \"nothing\")\n",
"list::class"
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],
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"hide_output_from_viewers": true
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"outputs": [],
"execution_count": null
},
{
"cell_type": "code",
"source": [
"\n",
"/**\n",
"* This one creates a mutable list\n",
"*/\n",
"val mutableList: MutableList<String> = mutableListOf(\"a\", \"b\", \"c\")\n",
"mutableList[2] = \"d\"\n",
"mutableList.add(\"e\")\n",
"mutableList += \"f\"\n",
"mutableList"
],
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"outputs": [],
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{
"metadata": {},
"cell_type": "code",
"source": [
"\n",
"//don't do that ever\n",
"fun doBadThingWithList(list: List<String>): List<String> = (list as MutableList<String>).apply { add(\"something\") }\n",
"\n",
"doBadThingWithList(listOf(\"a\", \"b\", \"c\"))"
],
"outputs": [],
"execution_count": null
},
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{
"cell_type": "code",
"source": [
"listOf(\"a\")::class"
],
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"node_id": "zKxwfvdRQwsgqRxK5GPTIK",
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"hide_output_from_viewers": true
}
},
"outputs": [],
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},
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{
"metadata": {},
"cell_type": "code",
"source": [
"val mutableList = mutableListOf(1,2,3)\n",
"\n",
"fun consumeList(list: List<Int>){\n",
" println(list.joinToString())\n",
"}\n",
"consumeList(mutableList)\n",
"mutableList.add(4)\n",
"consumeList(mutableList)"
],
"outputs": [],
"execution_count": null
},
{
"metadata": {},
"cell_type": "code",
"source": "listOf(1,2) + listOf(3,4)",
"outputs": [],
"execution_count": null
},
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{
"cell_type": "code",
"source": [
"var roList = listOf(\"a\", \"b\")\n",
"roList += setOf(\"c\")\n",
"roList"
],
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"datalore": {
"node_id": "yK6QD0dvrT98t7dx0pWJ5s",
"type": "CODE",
"hide_input_from_viewers": true,
"hide_output_from_viewers": true
}
},
"outputs": [],
"execution_count": null
},
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{
"metadata": {},
"cell_type": "code",
"source": [
"val writableList = mutableListOf(\"a\", \"b\") // Warning!\n",
"writableList += setOf(\"c\")\n",
"writableList"
],
"outputs": [],
"execution_count": null
},
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{
"cell_type": "code",
"source": [
"\n",
"/**\n",
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" * This one creates a mutable ArrayList.\n",
" */\n",
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"val arrayList: ArrayList<String> = arrayListOf(\"a\", \"b\", \"c\")\n",
"\n",
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"//ArrayList<Int>()\n",
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"\n",
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"//Danger zone\n",
"//\n",
"//val newList: List<String> = list + \"f\" + mutableList\n",
"//\n",
"//println(newList)"
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],
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"node_id": "qSaaZGyHiH9dsL4dtQ8UyE",
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"hide_input_from_viewers": true,
"hide_output_from_viewers": true
}
},
"outputs": [],
"execution_count": null
},
{
"cell_type": "code",
"source": [
"\n",
"//Bonus\n",
"\n",
"val lambdaList = List(3){ it.toString() }\n",
"println(lambdaList)\n",
"\n",
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"val builderList: List<Int> = buildList {\n",
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" add(2)\n",
" add(8)\n",
" remove(8)\n",
"}\n",
"builderList"
],
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"datalore": {
"node_id": "JPSYaCAgOZRveNdFPO15SG",
"type": "CODE",
"hide_input_from_viewers": true,
"hide_output_from_viewers": true
}
},
"outputs": [],
"execution_count": null
},
{
"cell_type": "code",
"source": [
"// val sequentialList = List(20){it}\n",
"// sequentialList.zipWithNext{ l, r -> r - l }.forEach{println(it)}"
],
"metadata": {
"datalore": {
"node_id": "fQBhhTBHCdc9JkWiMZ6uEh",
"type": "CODE",
"hide_input_from_viewers": true,
"hide_output_from_viewers": true
}
},
"outputs": [],
"execution_count": null
},
{
"cell_type": "markdown",
"source": [
"## Shortcut collection builders"
],
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"cell_type": "code",
"source": [
"/**\n",
" * Use shortcut function to provide default values\n",
" */\n",
"fun doSomething(additionalArguments: List<String> = emptyList()){\n",
" TODO()\n",
" emptyArray<String>()\n",
" emptySet<String>()\n",
" emptyMap<String,String>()\n",
"}\n",
"emptyList<String>()::class"
],
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"datalore": {
"node_id": "F5RQ5108YJe3pzfN0eAWwm",
"type": "CODE",
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"hide_output_from_viewers": true
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},
"outputs": [],
"execution_count": null
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{
"metadata": {},
"cell_type": "code",
"source": "",
"outputs": [],
"execution_count": null
},
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{
"cell_type": "markdown",
"source": [
"## Maps"
],
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"cell_type": "code",
"source": [
"val map = mutableMapOf(\n",
" \"key\" to \"a\",\n",
" \"key2\" to \"b\",\n",
")\n",
"\n",
"//The map could be accessed via indexing operation\n",
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"println(map::class)\n",
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"println(map[\"key\"])\n",
"map[\"key\"] = \"fff\"\n",
"println(map[\"key\"])\n",
"println(map[\"key3\"])"
],
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{
"cell_type": "code",
"source": [
"\n",
"//val entry: MutableMap.MutableEntry<String, String> = map.iterator().next()\n",
"\n",
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"//map.entries.first().component2()\n",
"\n",
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"/**\n",
" * The destructuring declaration for maps and other objects that support `operator fun componentN`\n",
" */\n",
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"for ((k: String, v) in map) {\n",
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"//val (k, v) = entry\n",
"// val k = entry.component1()\n",
"// val v = entry.component2()\n",
" println(\"$k -> $v\")\n",
"}"
],
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{
"cell_type": "code",
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"source": "map.forEach { (k, v) -> println(\"$k -> $v\")}",
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"metadata": {
"datalore": {
"node_id": "s1Q65aNWb9YNBZOgxmjotW",
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"hide_output_from_viewers": true
}
},
"outputs": [],
"execution_count": null
},
{
"cell_type": "code",
"source": [
"\n",
"val (a, b) = Pair(1, 2)\n",
"\n",
"val coord = doubleArrayOf(0.0, 1.0, 2.0)\n",
"\n",
"val (x,y,z) = coord\n",
"\n",
"data class Coordinate(val x: Double, val y: Int)\n",
"\n",
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"val (x1, y1) = Coordinate(1.0, 2)"
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],
"metadata": {
"datalore": {
"node_id": "t8YITxVsoTt7o9KnnOvO0Z",
"type": "CODE",
"hide_input_from_viewers": true,
"hide_output_from_viewers": true
}
},
"outputs": [],
"execution_count": null
},
{
"cell_type": "markdown",
"source": [
"## Mutable type access decorator\n",
"\n",
"To be replaced with qualified getter types soon"
],
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"cell_type": "code",
"source": [
"class AClassWithList{\n",
" var b: Double = 2.0\n",
" private set\n",
"\n",
" init{\n",
" b = 5.0\n",
" }\n",
"\n",
" private val _list: MutableList<Int> = ArrayList<Int>()\n",
" val list: List<Int> get() = _list\n",
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" \n",
" fun add(int: Int){\n",
" require(int>0)\n",
" _list.add(int)\n",
" }\n",
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"}\n",
"\n",
"\n",
"\n",
"val obj = AClassWithList()\n",
"\n",
"// obj.b = 10.0 //error\n",
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"obj.add(42)\n",
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"obj.list.add(43)"
],
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"hide_output_from_viewers": true
}
},
"outputs": [],
"execution_count": null
},
{
"cell_type": "markdown",
"source": [
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"## Wrap mutable logic"
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],
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2024-11-12 09:20:43 +03:00
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"cell_type": "code",
"source": [
"val list = buildList {\n",
" repeat(10){\n",
" add(it)\n",
" }\n",
"}\n",
"println(list)"
],
"metadata": {
"datalore": {
"node_id": "pJfVynao7enb7Q07lJRGRl",
"type": "CODE",
"hide_input_from_viewers": true,
"hide_output_from_viewers": true
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},
"outputs": [],
"execution_count": null
},
{
"metadata": {},
"cell_type": "code",
"source": [
"data class ImmutableObject(val a: String, val b: String, val c: Int)\n",
"\n",
"class ImmutableObjectBuilder(a: String) {\n",
" var a: String = a\n",
" var b: String = \"\"\n",
" var c = 0\n",
" \n",
" fun build() = ImmutableObject(a, b, c)\n",
"}\n",
"\n",
"fun ImmutableObject(a: String, block: ImmutableObjectBuilder.() -> Unit): ImmutableObject =\n",
" ImmutableObjectBuilder(a).apply(block).build()\n",
"\n",
"ImmutableObject(\"aValue\") {\n",
" c = 99\n",
"}"
],
"outputs": [],
"execution_count": null
},
{
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"hide_input_from_viewers": true,
"hide_output_from_viewers": true
}
},
"cell_type": "markdown",
"source": "## Contains operator and ranges"
},
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"cell_type": "code",
"source": [
"\n",
"val emailsList = emptyList<String>()\n",
"\n",
"// When used directly infix in operator checks if the element is contained in a collection\n",
"//using `operator fun contains`\n",
"\n",
"if (\"john@example.com\" in emailsList) {\n",
" println(\"is in list\")\n",
"}\n",
"\n",
"if (\"jane@example.com\" !in emailsList) {\n",
" println(\"not in list\")\n",
"}"
],
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"outputs": [],
"execution_count": null
},
{
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"metadata": {
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2024-11-12 09:20:43 +03:00
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2024-10-29 09:30:55 +03:00
"type": "CODE",
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"hide_output_from_viewers": true
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"cell_type": "code",
"source": [
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"import java.time.*\n",
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"\n",
"class DateRange(val start: Instant, val end: Instant)\n",
"\n",
"operator fun DateRange.contains(value: Instant): Boolean = value > start && value < end\n",
"\n",
"\n",
"println(Instant.now() in DateRange(Instant.EPOCH, Instant.MAX))"
],
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"outputs": [],
"execution_count": null
},
{
2024-10-29 09:30:55 +03:00
"metadata": {
"datalore": {
2024-11-12 09:20:43 +03:00
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2024-10-29 09:30:55 +03:00
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"cell_type": "code",
"source": [
"\n",
"// Another (different) use of `in` is iteration over range or collection using\n",
"// using `operator fun iterator`\n",
"\n",
"for (i in 1..100) {\n",
" println(i)\n",
"} // closed range: includes 100\n",
"\n",
"(1..100).forEach { i ->\n",
" println(i)\n",
"} //the same, but with boxing\n",
"\n",
"for (i in 1..<100) {\n",
" println(i)\n",
"} // half-open range: does not include 100\n",
"\n",
"for (x in 2..10 step 2) {\n",
" println(x)\n",
"}\n",
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"\n",
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"for (x in 10 downTo 1) {\n",
" println(x)\n",
"}\n",
"\n",
"infix fun ClosedRange<Double>.step(step: Double): Sequence<Double> {\n",
" //TODO check arguments\n",
" var current = start\n",
" return sequence {\n",
" do {\n",
" yield(current)\n",
" current += step\n",
" } while (current <= endInclusive)\n",
" }\n",
"}\n",
"\n",
"for (x in 0.0..10.0 step 0.5){\n",
" println(x)\n",
"}"
],
"outputs": [],
"execution_count": null
},
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2024-11-12 09:20:43 +03:00
},
"cell_type": "markdown",
"source": "## Map-reduce"
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},
{
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2024-10-29 09:30:55 +03:00
"cell_type": "code",
"source": [
"val list: List<Int> = listOf(1, 2, 3, 4, 5, 6)\n",
"\n",
"val result = list\n",
" //.stream().parallel()\n",
" //.asSequence()\n",
" .filter { it % 2 == 0 } //select even numbers\n",
" .map { it * it } // get square of each element\n",
" //.onEach { println(it) }\n",
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" //.sumOf { it } //use one of reduce operations\n",
" .reduce { acc: Int, i: Int -> acc + i }\n",
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"\n",
"result"
],
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"execution_count": null
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{
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2024-11-12 09:20:43 +03:00
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"source": [
"val sequence = sequence {\n",
" var counter = 1\n",
" while(true){\n",
" yield(counter++)\n",
" yield(counter++)\n",
" // println(counter)\n",
" }\n",
"}\n",
"\n",
"val result = sequence\n",
" .take(6)\n",
" .filter { it % 2 == 0 } //select even numbers\n",
" .map { it * it } // get square of each element\n",
" //.onEach { println(it) }\n",
" //.sumOf { it } //use one of reduce operations\n",
" .reduce { acc: Int, i: Int -> acc + i }\n",
"\n",
"result"
],
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{
"cell_type": "markdown",
"source": [
"## Scoped resource usage"
],
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"import java.nio.file.*\n",
"\n",
"\n",
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"val stream = Files.newInputStream(Paths.get(\"file.txt\"))\n",
"// The resource is automatically closed when leaving the scope\n",
"stream.bufferedReader().use { reader ->\n",
" println(reader.readText())\n",
"}"
],
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"cell_type": "markdown",
"source": [
"## Factory as parameter and companion factories"
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"interface Factory<T : Any> {\n",
" fun build(str: String): T\n",
"}\n",
"\n",
"data class IntContainer(val arg: Int) {\n",
" \n",
" companion object : Factory<IntContainer> {\n",
" override fun build(str: String) = IntContainer(str.toInt())\n",
"\n",
" fun buildSpecial(str: String) = IntContainer(str.toInt())\n",
" }\n",
"}\n",
"\n",
"data class DoubleContainer(val arg: Double) {\n",
" \n",
" companion object : Factory<DoubleContainer> {\n",
" override fun build(str: String) = DoubleContainer(str.toDouble())\n",
" }\n",
"}\n",
"\n",
"fun <T : Any> buildContainer(str: String, factory: Factory<T>): T = factory.build(str)\n",
"\n",
"\n",
"buildContainer(\"22\", IntContainer)\n"
],
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"source": [
"## Initialization"
],
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"\n",
"open class Bad{\n",
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" val value: Int = requestValue()\n",
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"\n",
" open fun requestValue(): Int {\n",
" doSomethingElse()\n",
" return 2\n",
" }\n",
"\n",
" private fun doSomethingElse(){\n",
" println(value)\n",
" }\n",
"}\n",
"\n",
"Bad()"
],
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2024-11-12 09:20:43 +03:00
{
"metadata": {},
"cell_type": "code",
"source": [
"class BadString{\n",
" val value: String = requestValue()\n",
"\n",
" fun requestValue(): String {\n",
" doSomethingElse()\n",
" return \"2\"\n",
" }\n",
"\n",
" private fun doSomethingElse(){\n",
" println(value)\n",
" }\n",
"}\n",
"\n",
"BadString()"
],
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"source": [
"\n",
"\n",
"//Factory functions are preferred to the initialization logic\n",
"\n",
"data class Good internal constructor(val value: Int){\n",
" init {\n",
" //Initialization block is there to check arguments\n",
" require(value >= 0)\n",
" }\n",
"\n",
" companion object\n",
"}\n",
"\n",
"fun requestValue(): Int = TODO()\n",
"\n",
"// This is the factory-function\n",
"fun Good() = Good(requestValue())\n",
"\n",
"\n",
"// additional constructor-like builders could be added to the companion\n",
"\n",
"@OptIn(ExperimentalUnsignedTypes::class)\n",
"fun Good.Companion.build(value: UInt) = Good(value.toInt())\n",
"\n",
"Good.build(32U)"
],
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"source": [
"## Delegates"
],
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"source": [
"class ClassWithALazyProperty{\n",
" //Use lazy delegate for something that should be calculated ones on first call\n",
" val lazyValue by lazy {\n",
" //Do dome heavy logic here\n",
" println(\"Initialized\")\n",
" 22\n",
" }\n",
"\n",
" val getterValue: Int get(){\n",
" println(\"got\")\n",
" return 33\n",
" }\n",
"}\n",
"val lazyClass = ClassWithALazyProperty()\n",
"lazyClass.lazyValue\n",
"lazyClass.lazyValue\n",
"lazyClass.getterValue\n",
"lazyClass.getterValue"
],
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"\n",
"//Using other delegates\n",
"val map = mutableMapOf(\"a\" to 1, \"b\" to 2)\n",
"\n",
"var a: Int by map\n",
"\n",
"println(a)\n",
"a = 3\n",
"println(map)"
],
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"source": [
"## Inline functions"
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"\n",
"/**\n",
" * Definition of inline function\n",
" */\n",
"inline fun List<Int>.forEachOdd(block: (Int) -> Unit) = forEach {\n",
" if (it % 2 == 1) block(it)\n",
"}\n",
"\n",
"\n",
"/**\n",
" * The demonstration of use of inline [forEach] function with non-local return\n",
" */\n",
"fun foo(): Int {\n",
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" listOf(1, 2, 3, 4, 5).forEachOdd {\n",
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" if (it == 3) return it // non-local return directly to the caller of foo()\n",
" print(\"$it, \")\n",
" }\n",
" println(\"this point is unreachable\")\n",
" return 0\n",
"}\n",
"foo()"
],
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"\n",
"/**\n",
" * Using inline function for type reification during the compile time\n",
" */\n",
"inline fun <reified T> List<T>.prettyPrint() = forEach {\n",
" when (T::class) {\n",
" Double::class -> println(\"Double: ${it as Double}\")\n",
" Int::class -> println(\"Int: ${it as Int}\")\n",
" else -> it.toString()\n",
" }\n",
"}\n",
"\n",
"inline fun <reified T> prettyPrintOne(arg: T) = listOf(arg).prettyPrint()\n",
"\n",
"listOf(1, 2, 3).prettyPrint()\n",
"\n",
"/**\n",
" * **WARNING** inline functions are an advanced feature and should be used only for\n",
" * reification or non-local return\n",
" * NOT for optimization.\n",
" */"
],
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"source": [
"## Collections and boxing"
],
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"/**\n",
" * Values are boxed. Each call is indirect\n",
" */\n",
"val list: List<Double> = List(20) { it.toDouble() }\n",
"\n",
"/**\n",
" * Still boxed\n",
" */\n",
"val genericArray: Array<Double> = Array(20) { it.toDouble() }\n",
"\n",
"/**\n",
" * Non-boxed\n",
" */\n",
"val specializedArray: DoubleArray = DoubleArray(20) { it.toDouble() }"
],
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