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Mastering Kotlin Essentials

Extension Functions and Object Declarations

Explore how to use extension functions in Kotlin to add functionality to classes and objects without altering original code. Learn the rules for defining extensions on companion objects and when to avoid member extension functions to maintain clean code.

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Extension functions on object declarations

We can define extensions on object declarations.

Kotlin 1.5
object A
fun A.foo() {
    print("\n Hi")
}
fun main() {
    A.foo()
    val a: A = A
    a.foo()
}

Extension

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