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.
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return (brackets are optional)
● is required in Block Syntax if Function returns value
● is forbidden in Assignment Syntax (single statement) & Lambda Expression Syntax
Return Data Type (brackets are optional)
● can be omitted in Block Syntax only Function returns no value (Unit Data Type)
● can be omitted in Assignment Syntax
Parameter Data Types can be omitted only if Anonymous Functions are stored in Variables declared with Signature.
Anonymous Functions
● can't have Default Values
● can't be called with Named Parameters
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Named Function Declaration
//DECLARE NAMED FUNCTION.
fun greet (name:String, age:Int = 20) : (String) { return("$name is ${age} years old.") }//Block
Syntax
fun greet (name:String, age:Int = 20) : (String) = "$name is ${age} years old." //Assignment
Syntax
fun greet (name:String, age:Int = 20) = "$name is ${age} years old." //Inferred return Data
Type
//CALL FUNCTION BY NAME.
greet(name="John", age=50) //Named Parameters (order not important)
greet("John", age=50) //Indexed before Named Parameters
greet("John", 50) //Indexed Parameters
greet("John") //Default Parameters after Indexed/Named
Params
Anonymous Function Declaration & Lambda Expression
//DECLARE VARIABLE.
var greet : (String, Int) -> (String) //Function Signature
//ANONYMOUS FUNCTION DECLARATION (store anonymous function into variable)
greet = fun (name:String, age:Int) : (String) { return("$name is ${age} years old.") } //Block Syntx
greet = fun (name:String, age:Int) : (String) = "$name is ${age} years old." //Assignment Syntax
greet = fun (name:String, age:Int) = "$name is ${age} years old." //Inferred return Data Type
greet = fun (name , age) = "$name is ${age} years old." //Inferred parameter Data Types
//LAMBDA EXPRESSION (store anonymous function into variable)
greet = { name:String, age:Int -> "$name is $age years old." } //Inferred return Data Type
greet = { name , age -> "$name is $age years old." } //Inferred parameter Data Types from greet var
//CALL FUNCTION THROUGH VARIABLE.
greet("John", 50) //No Default Values and Named Parameters
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Variable Number of Arguments
//DECLARE FUNCTION WITH VARARG PARAMETER.
fun sumOfNumbers(vararg numbers: Int, base: Int) : Unit {
var sum = base
for(number in numbers) { sum += number }
println(sum)
}
//CALL FUNCTION WITH VARIABLE NUMBER OF ARGUMENTS.
sumOfNumbers(1, 2, 3, 4, baseNumber = 10) //Other Parameters must be called with their names
//CALL FUNCTION WITH ARRAY ELEMENTS //var numbers : IntArray = intArrayOf(1, 2, 3, 4)
var numbers : Array<Int> = arrayOf<Int>(1, 2, 3, 4) //Use spread operator (*) to load
sumOfNumbers(*numbers.toIntArray(), base=10) //vararg Parameter with Array Elements
Function Scope
//===========================================================================================================
// DECLARE FUNCTIONS
//===========================================================================================================
fun topLevelFunction() { println("Top level Function") }
fun outerFunction() {
fun localFunction() { println("Local/Inner Function") } //Must be declared first
localFunction()
}
class Person {
fun memberFunction() { println("Member Function") }
}
fun Person.extensionFunction() { println("Extension Function") }
//===========================================================================================================
// CALL FUNCTIONS
//===========================================================================================================
fun main() {
topLevelFunction() //Top level Function
outerFunction() //Calls Local/Inner Function
var person = Person()
person.memberFunction() //Member Function (Method)
person.extensionFunction() //Extension Function
}
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Function as Input Parameter
//===========================================================================================================
// FUNCTION: executeFunction
//===========================================================================================================
fun executeFunction( receivedFunction: (name: String, age: Int) -> String ) {
var result = receivedFunction("John", 20)
println(result)
}
//===========================================================================================================
// FUNCTION: main
//===========================================================================================================
fun main() {
//DECLARE LOCAL VARIABLE
var weight = 150 //It is sent as Closure Property
//DECLARE FUNCTIONS.
fun namedFunction (name: String, age: Int) : String { return("$name is $age years old and $weight kg.")
}
var anonymFunc = fun (name: String, age: Int) : String { return("$name is $age years old and $weight kg.")
}
var lambdaFunc = { name: String, age: Int -> "$name is $age years old and $weight kg"
}
//USE FUNCTIONS AS PARAMETER (Sends Closure With Weight Property).
executeFunction(::namedFunction) //Function Name
executeFunction(anonymFunc) //Variable Name
executeFunction(lambdaFunc) //Variable Name
executeFunction( fun (name: String, age: Int) : String { return("$name is $age years old and $weight kg")
})
executeFunction( { name: String, age: Int -> "$name is $age years old and $weight kg" } ) //Lambda
}
Function as Return Value
//===========================================================================================================
//FUNCTION: getFunction
//===========================================================================================================
fun returnFunction ( weight: Int) : (name: String, age: Int) -> String {
return { name: String, age: Int -> "$name is $age years old and $weight kg" }
}
//===========================================================================================================
//FUNCTION: main
//===========================================================================================================
fun main() {
var returnedFunction = returnFunction(150) //Returns Closure with Weight Property already initialized
var result = returnedFunction("John", 20) //Call Function with missing Parameters
println(result)
}
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Infix Method
● must be member or extension functions
● must have single parameter (without default value or vargarg)
● can be called without '.' and brackets
Infix Method
//===========================================================================================================
// CLASS: Person
//===========================================================================================================
class Person(var age: Int) {
infix fun addAge(age: Int) : Int { return this.age + age } //must be member or extension functions
}
//===========================================================================================================
// FUNCTION: main
//===========================================================================================================
fun main() {
//CALL METHOD.
var person = Person(20)
var newAge = person.addAge(10) //Normal call
newAge = person addAge 10 //Infix call (must have single parameter without default value or vargarg)
//DISPLAY RESULT.
print(newAge)
}
