scala - 如何将 Scala 私有(private)范围限制为仅一个对象？

Question

我试图指定 val 常量仅对一个对象可见:

object Config {
    private[my.pack.MyObject] val Some = Option("String")
}

// in package my.pack
object MyObject {
    val Other = Config.Some
}

编译时出现错误:

[error] C:\path\Config.scala:17: ']' expected but '.' found.
[error]   private[my.pack.MyObject] val Some = Option("String")
[error]              ^

怎么了？当我读到访问限定符时，它们可以是类或对象，而不是包，我错了吗？

Answer 1

来自 the Scala Language specification, section 5.2.1 :

A private modifier can be qualified with an identifier C (e.g. private[C]) that must denote a class or package enclosing the definition. Members labeled with such a modifier are accessible respectively only from code inside the package C or only from code inside the class C and its companion module.

(大胆的我——注意“类或包”也承认“对象”，不确定这是规范中的标准语言，还是规范中的错误)

因此您的示例无法编译，因为 my.pack.MyObject 不是 val Some 的封闭声明。