具有地图功能的Scala Lambda函数 [英] Scala lambda function with map function

问题描述

我定义以下变量x

val x = Array((3,2), (4,5))

其类型为Array[(Int, Int)]

当我执行以下操作时:

x.map((a: Int, b: Int) => "(" + a + ", " + b + ")")

我收到以下错误:

console:28: error: type mismatch;
found   : (Int, Int) => String
required: ((Int, Int)) => ?
             x.map((a: Int, b: Int) => "(" + a + ", " + b + ")")

为什么期望第一个元素的类型为((Int, Int))?

Why does it expect the type of the first element to be ((Int, Int))?

推荐答案

(Int, Int) => ...是具有两个参数的函数的类型，两个参数都是Int(这是(a: Int, b: Int) => ...始终给出的).

(Int, Int) => ... is the type of a function with two arguments, both Int (and that's what (a: Int, b: Int) => ... will always give).

((Int, Int)) => ...是带有一个(Int, Int)自变量的函数的类型. Array上的map需要一个带有一个参数的函数，对于Array[(Int, Int)]，此参数的类型必须为(Int, Int).

((Int, Int)) => ... is the type of a function with one (Int, Int) argument. map on Array needs a function with one argument and for Array[(Int, Int)] the type of this argument must be (Int, Int).

所以您需要写

x.map(pair => "(" + pair._1 + ", " + pair._2 + ")")

其中pair具有类型(Int, Int)或

x.map { case (a, b) => "(" + a + ", " + b + ")" }

(使用模式匹配).请注意，在这种情况下，需要使用大括号.

(using pattern-matching). Note that in this case braces are required.

这篇关于具有地图功能的Scala Lambda函数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！