Elvis operator in Kotlin

This operator is a question mark followed by a colon (?:) with no space in between. It is named for an emoticon (short form of “emotion icon”) of the musician Elvis Presley, and is also a play on the words “else-if” (which sounds vaguely like “Elvis”)

A number of programming languages (eg. C#, TypeScript, etc) provide a null coalescing operator that performs the same action as Kotlin’s Elvis operator.

In Elvis operator, if the expression on the left of ?: is not null, that expression becomes the result. If the left-hand expression is null, then the expression on the right of the ?: becomes the result.

val len1: Int = if (b != null) b.length else -1

val len2: Int = b?.length ?: -1

The len1 is using if-else expression while len2 is using Elvis operator. They both will result in the same.