Kotlin Ternary Conditional Operator

Question

What is the equivalent of this expression in Kotlin?

a ? b : c 

This is not valid code in Kotlin.

Answer 1

In Kotlin, if statements are expressions. So the following code is equivalent:

if (a) b else c 

The distinction between expression and statement is important here. In Java/C#/JavaScript, if forms a statement, meaning that it does not resolve to a value. More concretely, you can't assign it to a variable.

// Valid Kotlin, but invalid Java/C#/JavaScript var v = if (a) b else c 

If you're coming from a language where if is a statement, this might seem unnatural but that feeling should soon subside.

Answer 2

TL;DR

if (a) b else c 

^ is what you can use instead of the ternary operator expression a ? b : c which Kotlin syntax does not allow.

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In Kotlin, many control statements, such as if, when, and even try, can be used as expressions. As a result, these statements can have a result which may be assigned to a variable, be returned from a function, etc.

Syntactically, there's no need for ternary operator

As a result of Kotlin's expressions, the language does not really need the ternary operator.

if (a) b else c 

is what you can use instead of the ternary operator expression a ? b : c.

I think the idea is that the former expression is more readable since everybody knows what ifelse does, whereas ? : is rather unclear if you're not familiar with the syntax already.

Nevertheless, I have to admit that I often miss the more convenient ternary operator.

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Other Alternatives

when

You might also see when constructs used in Kotlin when conditions are checked. It's also a way to express if-else cascades in an alternative way. The following corresponds to the OTs example.

when(a) {     true -> b     false -> c } 

Extensions

As many good examples (Kotlin Ternary Conditional Operator) in the other answers show, extensions can also help with solving your use case.