reserve various useful future keywords

[nikomatsakis]

I think we should reserve some keywords that we don't have specific uses for but which seem like they would generally be handy:

• where
• my
• our
• their
• not sure what else
• imm for immutable/immutably/etc (pnkfelix, 2013nov07)

Nominating.

cc @pnkfelix

[nikomatsakis]

Another suggestion: once (is this already reserved?)

[thestinger]

Yeah, once is already considered a real keyword (not just a reserved one).

[nikomatsakis]

It occurs to me that proper language versioning might be the right sol'n here. Java has managed to add keywords with (relatively) little pain, for example.

[pnkfelix]

Language Version markers is issue #3392

[liigo]

+1 for 'where' as a reserved keyword

[pnkfelix]

Accept that we will decide for 1.0. P-backcompat-lang.

[ghost]

otherwise like in Haskell.

[huonw]

@Jurily otherwise is actually just a normal identifier, but is given the value True in the prelude to act as "sugar": http://hackage.haskell.org/package/base-4.6.0.1/docs/src/GHC-Base.html#otherwise

[glaebhoerl]

I did some research looking at other languages' keywords and a list of most common English words for likely candidates.

Generally useful parts of speech (like where and for):

• from, into, is, of, on, out, to, with

Things Rust doesn't have at the moment but conceivably could, and/or has in the past, and/or which have come up in discussions:

• class, dynamic, friend, goto, lazy, new, pure, union, volatile

Exception handling:

• try, catch, finally, throw, throws

Generally useful keywords from other languages which haven't found a home in Rust (and are too long anyways):

• default, explicit, implicit

Keywords for things Rust has different (better:) solutions, words, and/or syntax for, and is unlikely to ever want, listed only in case someone else thinks differently:

• alias, auto, begin, case, const, data, def, delegate, delete, end, final, nil, null, object, operator, override, switch, synchronized, then, unless, until, var, void

[thestinger]

I think language versions would be a much better solution than this. It's already getting to the point where very common words are reserved just because. It's annoying enough to need to come up with alternatives to words like loop, but if there are no common words to use at all...

[pnkfelix]

If we do end up snagging more reserved words (though I agree that proper language versioning would be cleaner), I just wanted to add safe to the mix (as in, the opposite of unsafe).

[bjadamson]

raise

[brson]

I'm also concerned about the future need for safe.

[glaebhoerl]

By the way, with respect to typeof, if we ever add it, couldn't we re-use the existing type keyword instead?

[aturon]

Nominated. I recall discussing this a couple months ago. Either this should be closed, or it should be on the 1.0 milestone.

[pnkfelix]

closing; we'll attack each future keyword as it comes up, but just reserving a laundry list is not an idea we want to consider further