Extension functions in Kotlin

Add member-looking functions to types you do not own.

// An extension adds a member-looking function to a type you don't own.
fun String.shout() = uppercase() + "!"

fun Int.toElevationNote(): String =
    if (this > 2400) "$this m: thin air" else "$this m: easy breathing"

fun main() {
    println("summit day".shout())
    println(2650.toElevationNote())
    println(900.toElevationNote())
}

How it works

1. fun String.shout() makes "summit day".shout() legal.
2. Inside the body, this (implicit or spelled) is the receiver.
3. 2650.toElevationNote() reads like the Int always had the method.

Keywords and builtins used here

• String
• else
• fun
• if
• main
• shout
• this
• toElevationNote

The run, in numbers

Lines

11

Characters to type

324

Tokens

79

Three-star pace

70 tpm

At the three-star pace of 70 tokens a minute, this run takes about 68 seconds.

Type this snippet

Step 3 of 3 in Functions, step 9 of 27 in Language basics.

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