Scala - 推断类型参数 [英] Scala - infer type parameters

问题描述

为什么这段代码会产生错误

Why does this code produce an error

def test[A](a: List[A], f: A => A) = a.map(f)

println(test(List(1,2,3), _*2))

error: missing parameter type for expanded function ((x$2) => x$2.$times(2))

Scala 不应该知道 A 是 Int 吗?

shouldn't Scala be able to tell that A is Int?

推荐答案

您需要第二个参数列表才能工作.我不确定规范中是如何定义的，但我以前见过这个.

You need a second parameter list for this to work. I'm not sure how this is defined in the spec, however I have seen this before.

scala> def test[A](a: List[A])(f: A => A) = a.map(f)
test: [A](a: List[A])(f: (A) => A)List[A]

scala> test(List(1))(_+1)
res1: List[Int] = List(2)

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