为什么 apply() 不能在包对象上以简写形式使用? [英] Why apply() can not be used in shorthand form on package objects?

问题描述

在普通对象上，我可以执行以下操作:

On normal objects, I can do the following:

object A {
  def apply = "!"
}
A() // "!"

但是在包对象上，这不起作用:

But on package objects, this doesn't work:

package object A {
  def apply = "?"
}
A.apply // "?"
A() // compile error
    // error: package A is not a value

有什么基本的限制吗?或者这只是一个实现限制，我可以通过稍微调整编译器来解决?

Is there some fundamental limitation? Or is it just an implementation limitation, which I can fix by tweaking the compiler a bit?

推荐答案

唯一可以不用申请的方法是:

The only way you can do it without apply is this:

A.`package`()

这是因为 A 不表示值或方法，并且语言规范指出对于 f() 是有效的，f 必须有一个方法类型或一个带有 apply 方法的值类型.我不知道调整"编译器来改变这一点有多容易，但我怀疑这是否值得付出努力.如果您确实想达到这样的长度，只需将您的方法添加到 Predef 中会更容易.

This is because A does not denote a value or a method, and the language specification states that for f() to be valid, f has to have a method type or a value type with an apply method. I have no idea how easily one could "tweak" the compiler to change this, but I doubt it's worth the effort. If you do want to go to such lengths, it would be easier to just add your method to Predef.

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