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What is the purpose of trailing lambda syntax (Kotlin)?

Passing a lambda to the last parameter

In Kotlin, there is a convention that if the last parameter of a function accepts a function, a lambda expression that is passed as the corresponding argument can be placed outside the parentheses:

val product = items.fold(1) { acc, e -> acc * e }

What is the purpose of this syntax?

Solution

  • This syntax gives Kotlin great DSL capabilities, it makes functions look like language constructions. For example:

    with(car) {
   startUp()
   goToDestination()
}

    Here with looks like it is language construction, whereas it is a simple function, receiving lambda as the last parameter.

    And this leads to such elegant things like Kotlin HTML DSL