箭头(“->")运算符在Kotlin中做什么? [英] What does the arrow ("->") operator do in Kotlin?

问题描述

可能有一个广泛的问题，但官方文档甚至没有提到箭头运算符(或语言构造，我不知道哪个短语更准确)作为独立实体.

Probably a little bit broad question, but the official documentation doesn't even mentioning the arrow operator (or language construct, I don't know which phrase is more accurate) as an independent entity.

最明显的用途是when条件语句，该语句用于将表达式分配给特定条件:

The most obvious use is the when conditional statement, where it is used to assign an expression to a specific condition:

  val greet = when(args[0]) {
    "Appul" -> "howdy!"
    "Orang" -> "wazzup?"
    "Banan" -> "bonjur!"
    else    -> "hi!"
  }

  println(args[0] +" greets you: \""+ greet +"\"")

其他用途还有什么? Kotlin中的箭头运算符是否有一般含义?

What are the other uses, and what are they do? Is there a general meaning of the arrow operator in Kotlin?

推荐答案

->是Kotlin语法的一部分(类似于Java的

The -> is part of Kotlin's syntax (similar to Java's lambda expressions syntax) and can be used in 3 contexts:

• when表达式，其中将匹配/条件"部分与结果/执行"块分开

• when expressions where it separates "matching/condition" part from "result/execution" block

 val greet = when(args[0]) {
   "Apple", "Orange" -> "fruit"
   is Number -> "How many?"
   else    -> "hi!"
 }

lambda表达式，它将参数与函数体分开

lambda expressions where it separates parameters from function body

  val lambda = { a:String -> "hi!" }
  items.filter { element -> element == "search"  }

函数类型，其中将参数类型与结果类型分开，例如comparator

  fun <T> sort(comparator:(T,T) -> Int){
  }

有关Kotlin语法的详细信息，请参见文档中的 :

Details about Kotlin grammar are in the documentation in particular:

• functionType
• functionLiteral
• whenEntry

• functionType
• functionLiteral
• whenEntry

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