file-private should have its own keyword so we can...

# language-proposals

[Miguel Vargas]

file-private should have its own keyword so we can designate class members as file-private

package a

class B {
  // only accessible from within this file
  file-private val priv = 123
}

fun c(b: B) {
  println("I can access ${b.priv}")
}

[Miguel Vargas]

This allows file private to be more of a replacement for java’s package-private

[jw]

STRONG agree. Love this from Swift.

[jw]

Note that Swift uses fileprivate, and visually I like it better due to lack of hyphen. Also not sure if the hyphen would introducer parser ambiguities or not.

[louiscad]

No ambiguity in a class/object declaration since you can't use subtraction there.

Visibility modifiers are already not supported in function bodies, where subtraction can happen.

[jw]

Sorry it's the lexer not the parser

[Miguel Vargas]

fileprivate also follows existing compound keyword convention such as typealias

[Ben Woodworth]

What about something like labeled visibility modifiers, like private@file?

Extend this notation to target specific types to also be visible from (similar to friend classes in C++)

class A {
    private@AFriend val something: String = "something"
}

class AFriend {
    fun getSomething(a: A): String = a.something
}

And if Kotlin ever gets union types:

internal typealias Alphabet = A | B | C
// use private@Alphabet

[Ben Woodworth]

(of course, you could just have all the 'friend' classes/members in the same file and a fileprivate keyword would be plenty)

[Klitos Kyriacou]

If we were to have fileprivate, should we also have filesealed?

[jw]

No? How is that different than fileprivate sealed class?

[Klitos Kyriacou]

I think fileprivate sealed class would make the class only accessible to other code in the same file. On the other hand, filesealed would make the class only extendable by other classes in the same file, but the class would be visible outside of that file. That would be the equivalent of Java's sealed classes with the permits clause naming only the classes in the same file.

[jw]

Seems like an orthogonal concern to visibility then. And I would prefer the permits approach rather than conflating it with visibility / location.

[Ben Woodworth]

Couldn't you just give the sealed class a fileprivate constructor?