Function References क्या हैं

एक function reference आपको किसी पहले से मौजूद function को नाम से इशारा करने देता है और इसे दो colons का उपयोग करके एक value की तरह सौंपने देता है।

In this page:

Referencing a Top-Level Function
Referencing a Member Function on an Instance
Referencing a Member Function on a Class
Constructor References

Syntax

kotlin

list.filter(::topLevelFunction)          // top-level function
list.forEach(instance::method)           // bound to an instance
list.map(ClassName::method)              // receiver comes from each element

Referencing a Top-Level Function

::functionName किसी मौजूदा standalone function को refer करता है, इसे किसी lambda में wrap किए बिना, जहां भी एक matching function type की उम्मीद हो वहां सीधे पास होने देते हुए।

उदाहरण: Referencing a Top-Level Function

markup

// Define the function `isEven` taking `n` and returning a `Boolean`
fun isEven(n: Int): Boolean = n % 2 == 0

// Entry point: execution of the program starts here
fun main() {
    // Declare a read-only variable `numbers`, set to `listOf(1, 2, 3, 4, 5, 6)`
    val numbers = listOf(1, 2, 3, 4, 5, 6)
    // Declare a read-only variable `evens`, set to `numbers.filter(::isEven)`
    val evens = numbers.filter(::isEven)
    // Print `evens` to the console, with a trailing newline
    println(evens)
}

Referencing a Member Function on an Instance

instance::method उस specific object से बंधा एक member function का bound reference बनाता है, सीधे एक function value की तरह उपयोग करने योग्य।

उदाहरण: Referencing a Member Function on an Instance

markup

// Define a class `Greeter`
class Greeter(val greeting: String) {
    fun greet(name: String) = "$greeting, $name!"
}

// Entry point: execution of the program starts here
fun main() {
    // Declare a read-only variable `greeter`, set to `Greeter("Hi")`
    val greeter = Greeter("Hi")
    // Declare a read-only variable `greetFn` (a `(String) -> String`), set to `greeter::greet`
    val greetFn: (String) -> String = greeter::greet
    // Print `greetFn("Kotlin")` to the console, with a trailing newline
    println(greetFn("Kotlin"))
}

Referencing a Member Function on a Class

ClassName::method एक unbound reference बनाता है, जहां reference असल में call होने पर receiver instance को पहले argument के रूप में देना चाहिए।

उदाहरण: Referencing a Member Function on a Class

markup

// Define a data class `Person`
data class Person(val name: String) {
    fun shout() = name.toUpperCase()
}

// Entry point: execution of the program starts here
fun main() {
    // Declare a read-only variable `shoutFn` (a `(Person) -> String`), set to `Person::shout`
    val shoutFn: (Person) -> String = Person::shout
    // Print `shoutFn(Person("ana"))` to the console, with a trailing newline
    println(shoutFn(Person("ana")))
}

Constructor References

::ClassName किसी class के constructor का एक reference बनाता है, जिसे बिल्कुल नए instances बनाने वाले एक function की तरह उपयोग किया जा सकता है।

उदाहरण: Constructor References

markup

// Define a data class `Point`
data class Point(val x: Int, val y: Int)

// Entry point: execution of the program starts here
fun main() {
    // Declare a read-only variable `coordinates`, set to `listOf(1 to 2, 3 to 4)`
    val coordinates = listOf(1 to 2, 3 to 4)
    // Declare a read-only variable `points`, set to `coordinates.map { (x, y) -> Point(x, y) }`
    val points = coordinates.map { (x, y) -> Point(x, y) }
    // Print `points` to the console, with a trailing newline
    println(points)
}

Chapter Quiz — Complete all 6 topics to unlock

0/6 topics done

Complete these topics first:

← Previous Lesson The it Keyword Next Lesson → Inline Functions

Function References क्या हैं

Referencing a Top-Level Function

Referencing a Member Function on an Instance

Referencing a Member Function on a Class

Constructor References

Chapter Quiz — Complete all 6 topics to unlock

Login to run this code