Home / Questions / 138223
Accepted
Alvaro Montoro
Asked: 2020-02-14 09:01:43 +0800 CST 2020-02-14 09:01:43 +0800 CST

What is `it` in Kotlin?

  • 772

For example, filling a crash array with data from another array:

if (datosAccidente.desperfectos.isNotEmpty()) {
  rDesperfectos = datosAccidente.desperfectos.map { Desperfecto(it) }
}

or when reading lines from a file:

File("./miFichero.txt").forEachLine { println(it) }

What is it itand what would it represent in those examples?

Reading the documentation , it is mentioned that it itis an implicit name for a single parameter, but then why wouldn't it work for a case like the following:

fun test(datos: String) {
  var aux: String = it
}
kotlin

1 Answers

  1. Best Answer

    In the documentation you linked it says:

    A lambda expression or an anonymous function is a "function literal"

    A lambda expression or anonymous function is a "literal function"

    And in the definition of itexplains:

    One other helpful convention is that if a function literal has only one parameter, its declaration may be omitted (along with the ->), and its name will beit

    Another useful convention is that if a literal function has only one parameter, its declaration can be omitted (along with the ->) and its name will beit .

    Therefore itit is a convention to make the declaration of lambda functions even shorter.

    This does not work with the function declared in the classic way

    fun test(datos: String) {
  var aux: String = it
}

    because the syntax explicitly requires the variable name and its type : The test function can be used in a general way, so the compiler cannot infer the type if it is not defined at this time, whereas lambda functions are declared in the moment in which they are going to be used (they have a very defined context) and, therefore, the type does not have to be defined explicitly.

    • 5