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What does 'by' keyword do in Kotlin?
Kotlin supports delegation of design pattern by introducing a new keyword "by". Using this keyword or delegation methodology, Kotlin allows the derived class to access all the implemented public methods of an interface through a specific object.
Example
In this example, we will implement an abstract method of a Base class from another class.
interface Base { //abstract method fun printMe() } class BaseImpl(val x: Int) : Base { // implementation of the method override fun printMe() { println(x) } } // delegating the public method on the object b class Derived(b: Base) : Base by b fun main(args: Array<String>) { val b = BaseImpl(10) // prints 10 :: accessing the printMe() method Derived(b).printMe() }
Output
It will produce the following output
10
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