Kotlin的折痕是什么允许我将运算函数放在右括号后面? [英] What is it about Kotlin's fold that allows me to put the operation function after the closing parentheses?

问题描述

在Kotlin中有关Iterable.fold(...)的事情是什么，允许我将operation函数放在后的右括号内?

What is it about Iterable.fold(...) in Kotlin that allows me to put the operation function after the closing parentheses?

val numbers = listOf(5, 2, 10, 4)

// operation function passed as the second param of fold
val sumDoubled1 = numbers.fold(0, { sum, n -> sum + n * 2 })
println(sumDoubled1)

// operation function after the closing paren of fold
val sumDoubled2 = numbers.fold(0) { sum, n -> sum + n * 2 }
println(sumDoubled2)

推荐答案

它称为

It is called Passing trailing lambdas means, if a methods takes last parameter input as function(aka method literal) then it can be placed outside that method call though you can also place it inside the brackets as well. A simple example would be:

fun main() {
    processInput("Lambda", { println(it) })
    processInput("Passing trailing lambda") { println(it) }
    processInput("Passing trailing lambda with named param") { input -> println(input) }
}

fun processInput(input:String, method:(str:String)->Unit){
    method(input.toUpperCase()) // additional logic
}

输出:

LAMBDA
PASSING TRAILING LAMBDA
PASSING TRAILING LAMBDA WITH NAMED PARAM

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