Kotlin is a powerful programming language that offers many features to make development faster and easier. One of these features are extension functions and properties.
Extension functions and properties allow you to extend the functionality of a class without having to inherit from it. This is especially useful when you want to use features from a library without depending on that library.
In this article, we'll take a closer look at extension functions and properties in Kotlin. We'll learn how to define them and how to use them in our own code.
Extension functions and properties are defined using the fun
and val
keywords, respectively. They are written after the name of the class that they are extending, followed by a dot .
:
// Extension function
fun String.repeat(times: Int): String {
return this.repeat(times)
}
// Extension property
val String.length: Int
get() = this.length
In the example above, we've defined an extension function repeat
that allows us to repeat a string a given number of times. We've also defined an extension property length
that allows us to get the length of a string.
Note that extension functions and properties are not actually defined in the class that they are extending. They are compiled as static methods and properties in the class that they are defined in. This means that they can be called from anywhere, even from outside of the class.
Extension functions and properties can be used just like any other function or property. In the example below, we use the repeat
function to repeat a string 10 times:
fun main() {
val s = "Hello, world!".repeat(10)
println(s)
}
We can also use the length
property to get the length of a string:
fun main() {
val s = "Hello, world!"
println(s.length)
}
It's also possible to override extension functions and properties. This can be useful when you want to change the behavior of a function or property in a specific context.
To override an extension function or property, you just need to define it in the same way as you would any other function or property. In the example below, we override the repeat
function so that it returns a string with the given number of exclamation points:
fun main() {
fun String.repeat(times: Int): String {
return this + "!".repeat(times)
}
val s = "Hello, world!".repeat(10)
println(s)
}
Extension functions and properties are a powerful feature in Kotlin that can be used to extend the functionality of a class without having to inherit from it. They are defined using the fun
and val
keywords, respectively, and they are written after the name of the class that they are extending, followed by a dot .
Extension functions and properties can be used just like any other function or property. They are compiled as static methods and properties, which means that they can be called from anywhere, even from outside of the class.
It's also possible to override extension functions and properties. This can be useful when you want to change the behavior of a function or property in a specific context.