rename Void => Nothing with alias Cvoid = Nothing

[StefanKarpinski]

This was discussed previously a few times. The Void name only really makes sense in the context of interop with C, for which the name Cvoid is better. We have a pretty well-established convention that name is an element of type Name so nothing :: Void is a bit of a surprising gotcha. Way back when, this type was called Nothing but it was deemed that we had too many kinds of nothingness, but we're really jumped the shark on that at this point.

[StefanKarpinski]

I will take a look at this and see if it feels better or not. Milestoning just as a reminder.

[StefanKarpinski]

Based on the PR sketching this out, I'm not sure if this churn is really worth it.

[StefanKarpinski]

Since I'm the one who opened this and I don't care for it, I guess I'll just close this.

[nalimilan]

Hey, you've got +11 vs -1, so I think it's worth it (but after the PR removing Nullable is merged...).

[StefanKarpinski]

Sure, I suppose I could reopen. It's just a lot of churn...

[Sacha0]

Crossposting my comment in #25097:

Much thanks for exploring this change concretely @StefanKarpinski! For what it's worth, having just looked over this branch I quite like it. The relationship between nothing and Void confused me when I came to Julia, and these changes completely eliminate that source of confusion. Additionally, I find the Ptr{Void} -> Ptr{Cvoid} changes beautifully clarifying as well. ❤️!

[iamed2]

I've also had this dream for a while:

convert(::Type{Void}, x) = nothing

function doesnt_return_anything(x, y)::Void
    something!(x, y)
end

which would be possible if Void was freed up. Then Void could be a "void" that you put stuff in and never get out 😄

[StefanKarpinski]

You can already do the above by defining:

convert(::Type{Void}, x) = nothing

function doesnt_return_anything(x, y)::Void
    something!(x, y)
end

Of course, the danger here is that with that convert definition this would silently work:

Void[1, 2, 3]

and produce an array of three nothings.