Kotlin elvis operator ?:

?:



• Symbol for elvis operator is ?:
• The elvis operator couples with safe call operator ?.
• Elvis operator returns the value to it's left if value is not null, else it returns the value to it's right

var foo = a ?: b

Here, if a is null, b is returned. If a is not null, a is returned.
Another elaborate example:

var msg: String?
msg = null

// use elvis operator
var msgLength1 = msg?.length ?: 0

// use traditional null check 
var msgLength2: Int
if (msg != null) {
  msgLength2 = msg.length
} else {
  msgLength2 = 0
}

println(msgLength1) // 0
println(msgLength2) // 0

In above code snippet, calculate of msgLength1 using safe call operator and elvis operator is same as calculation of msgLength2 using traditional conditional check.