Rename unused to ghost

[nicolasstucki]

No description provided.

[allanrenucci]

Any chance to pick another name, maybe even before the release, since apparently nobody likes unused?

I wouldn't make such a claim. Only one person complained which for me is more a sign that the name is not that controversial.

Personally, I prefer unused. I would discuss this a little more before settling on a new name. Maybe create a new topic in https://contributors.scala-lang.org/

[nicolasstucki]

I would change it to ghost as it is less controversial and does not clash whit any other concept we have in the language. It also highlights the link with phantom types. We can later create a topic on it to see which keyword should be used.

[Blaisorblade]

LGTM — both the changes and the strategy. Thanks for the prompt PR!

Given the size of the rename, I looked at current occurrences of unused, and comparing them with the ones before unused was merged. I used
vimdiff <(git grep unused compiler) <(git grep unused 2a85106974ce5620eabbf4658810ddb917465145 compiler), and inspecting the output of git grep unused.

I like the strategy — either way we might still change the name, but at least the one we use has no obvious blockers.

I wouldn't make such a claim. Only one person complained which for me is more a sign that the name is not that controversial.

"Nobody" was hyperbole, but based on comments by both Martin and IIRC Nicholas (apart from me).

[Blaisorblade]

I just merged this, also to unblock the release (let me know if I was too hasty).

For future discussion: the concept of "ghost" is also used by Liquid Haskell (and maybe @gsps's Liquid Scala), but for essentially the same thing: values that don't exist at runtime.

So maybe @gsps is also interested?

[biboudis]

It is also related to F*'s Ghost monad and erased type (Sec. 4).

https://www.fstar-lang.org/papers/mumon/paper.pdf

[joan38]

@allanrenucci Have you seen the poll: https://goo.gl/forms/UD44AfLUD3dkfnxs2 ?