Named Arguments

As with most other programming languages (Java, C++, etc.), Kotlin supports passing arguments to methods and constructors according to the order they are defined. Kotlin also supports named arguments to allow clearer invocations and avoid mistakes with the order of arguments. Such mistakes are hard to find because they are not detected by the compiler, for example, when two sequential arguments have the same type.

fun format(userName: String, domain: String) = "$userName@$domain"

fun main() {
    println(format("mario", "example.com"))                         // 1
    println(format("domain.com", "username"))                       // 2
    println(format(userName = "foo", domain = "bar.com"))           // 3
    println(format(domain = "frog.com", userName = "pepe"))         // 4
}

1. Calls a function with argument values.
2. Calls a function with switched arguments. No syntax errors, but the result domain.com@username is incorrect.
3. Calls a function with named arguments.
4. When invoking a function with named arguments, you can specify them in any order you like.