Return values
- Kotlin course
- Beginner
- Lesson 72/116
- 4 min
Learn to return a value from a function with return.
Return values: return and return type
A function can return a value. The return type is written after the parameter parentheses as : Type; the body uses return value to exit. Functions that return no value have return type Unit (or it is omitted).
fun add(a: Int, b: Int): Int {
return a + b
}
val sum = add(3, 4) // 7return exits the function and hands the value to the caller. In Unit-returning functions return is either value-less or not used.
Unit and implicit return
If a function returns no value, its return type is Unit. Writing Unit is optional; fun greet(name: String) { println(name) } actually means fun greet(name: String): Unit { ... }.
fun greet(name: String): Unit {
println("Hello $name")
}
// Omitting Unit means the sameprintln itself returns Unit. So a line that calls println has the value Unit; assigning it to another variable is meaningless.
Practice Define square and call it
Define a fun square(x: Int): Int whose body is return x * x. From main print the result with println(square(5)).
Starter code
fun main() {
// Print the square(5) call with println
}
// Define square: Int parameter, returns Int, returns x * xSample solution
fun main() {
println(square(5))
}
fun square(x: Int): Int {
return x * x
}Expected output
25
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does fun square(x: Int): Int { return x * x } return?
- String
- Unit
- Int Correct answer
- Boolean
Explanation: The return type is declared Int; x * x is an Int.
2 Match expression to role
| Term | Meaning |
|---|---|
return x + y |
Returns the value |
: Int |
Return type Int |
: Unit |
Returns no value |
return (alone) |
Exits the block |
3 Fill in the blank: return the value
fun add(a: Int, b: Int): Int { ____ a + b }fun add(a: Int, b: Int): Int { return a + b }Explanation: return a + b hands the value to the caller.