在 map、flatmap、...偏函数中使用元组 [英] Using Tuples in map, flatmap,... partial functions

问题描述

如果我这样做:

val l = Seq(("un", ""), ("deux", "hehe"), ("trois", "lol"))
l map { t => t._1 + t._2 }

没关系.

如果我这样做:

val l = Seq(("un", ""), ("deux", "hehe"), ("trois", "lol"))
l map { case (b, n) => b + n }

没关系.

但如果我这样做:

val l = Seq(("un", ""), ("deux", "hehe"), ("trois", "lol"))
l map { (b, n) => b + n }

它不会起作用.
为什么要使用case"关键字来使用命名元组?

It will not work.
Why should I use "case" keyword to use named tuples?

推荐答案

2.11的错误信息解释性更强:

The error message with 2.11 is more explanatory:

scala> l map { (b, n) => b + n }
<console>:9: error: missing parameter type
Note: The expected type requires a one-argument function accepting a 2-Tuple.
      Consider a pattern matching anonymous function, `{ case (b, n) =>  ... }`
              l map { (b, n) => b + n }
                       ^
<console>:9: error: missing parameter type
              l map { (b, n) => b + n }
                          ^

对于申请，您将获得自动元组":

For an apply, you get "auto-tupling":

scala> def f(p: (Int, Int)) = p._1 + p._2
f: (p: (Int, Int))Int

scala> f(1,2)
res0: Int = 3

你提供了两个参数而不是一个.

where you supplied two args instead of one.

但您不会自动取消配对.

But you don't get auto-untupling.

人们一直希望它以这种方式工作.

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