为什么这个通配符函数告诉我它有错误数量的参数? [英] Why does this wildcarded function tells me it has the wrong number of parameters?

问题描述

违规代码是:

<console>:47: error: wrong number of parameters; expected = 2
            terms.foldLeft(r.unitA)(r.add(_, _.eval(x)))

我通过写作解决了我的问题:

I solved my problem by writing:

 terms.foldLeft(r.unitA)((a,b) => r.add(a, b.eval(x)))

但我仍然想知道是什么阻止了我最初的尝试?

But I'd still like to know what prevented my initial attempt?

推荐答案

以下是 SLS 6.23 的部分:

Here is the section of the SLS 6.23:

http://iainmcgin.github.io/scala-ref-markdown/#placeholder-syntax-for-anonymous-functions

更新链接:

http://www.scala-lang.org/files/archive/spec/2.11/06-expressions.html#placeholder-syntax-for-anonymous-functions

Daniel Sobral 的帖子说:

Daniel Sobral's post says:

"当您使用_"作为匿名参数的占位符时函数，该函数的作用域是最里面的括号包含它.大部分时间.

"When you use "_" as a place holder for an anonymous parameter of a function, the scope of that function is the innermost parenthesis containing it. Most of the time.

更新自旋:我认为规范中的语法解释更容易获得，占位符不会转义封闭的 Expr.有各种重复的问题.

Updated spin: I think the syntax explanation from the spec is easier to get, that the placeholder doesn't escape an enclosing Expr. There are various duplicate questions.

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