Mastering Kotlin Essentials/

...

/

Single-Expression Functions vs. Functions on All Levels

Single-Expression Functions vs. Functions on All Levels

Explore function types by comparing single-expression and many-level approaches, and understand function levels, parameters, arguments, return types, and varargs.

We'll cover the following...

Single-expression functions

Many functions in real-life projects just have a single expressionAs a reminder, an expression is a part of our code that returns a value., so they start and immediately use the return keyword. The square function defined below is a great example. For such functions, instead of defining the body with curly braces, we can use the equality sign (=) and just specify the expression that calculates the result without specifying return. This is single-expression syntax, and functions that use it are called single-expression functions.

Press + to interact
fun square(x: Double): Double = x * x
fun main() {
    println(square(10.0)) // 100.0
}

An expression can be more complicated and take multiple lines. This is fine as long as its body is a single statement.

Press + to interact
fun findUsers(userFilter: UserFilter): List<User> =
    userRepository
        .getUsers()
        .map { it.toDomain() }
        .filter { userFilter.accepts(it) }

When we use single-expression function syntax, we can infer the result type. We don’t need to, but we can, even though explicit result types might still be useful for safety and readability.

Press + to interact
fun square(x: Double) = x * x
fun main() {
    println(square(10.0)) // 100.0
}
...