How restrict scala private scope to one object only?

Question

I am trying to specify that val constant is visible only to one object:

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

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

While compiling this I get an error:

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

What is wrong? As I read about access qualifiers they can be a class or object, not a package, am I wrong?

So you want to restrict access to val Some to an object other than the assigning object? I may be just confused, but should Config be able to assign a value to Some when it has no access to it? Can you explain a bit more about the use case? — Sascha Kolberg
– Sascha Kolberg, Commented Aug 30, 2015 at 9:00
That would be pretty weird if you could do scoping such that the Config object doesn't have access to its own val. — Chris Martin
– Chris Martin, Commented Aug 30, 2015 at 9:38

sjrd · Accepted Answer · 2015-08-30 09:36:45Z

6

From 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.

(bold mine -- note that "class or package" also admits "object", not sure if this is standard language in the spec, or a bug in the spec)

So your example does not compile because my.pack.MyObject is not an enclosing declaration of val Some.

answered Aug 30, 2015 at 9:36

sjrd

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