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Add docs for "!" Never type (rfc 1216) #35286

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merged 1 commit into from
Sep 29, 2016
Merged

Add docs for "!" Never type (rfc 1216) #35286

merged 1 commit into from
Sep 29, 2016

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dns2utf8
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@dns2utf8 dns2utf8 commented Aug 4, 2016

Pull Request: rust-lang/rfcs#1216
Tracking Issue: #35121

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r? @steveklabnik

(rust_highfive has picked a reviewer for you, use r? to override)

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dns2utf8 commented Aug 4, 2016

r? @nikomatsakis

apasel422
apasel422 reviewed Aug 4, 2016
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src/doc/book/syntax-index.md
@@ -162,6 +162,7 @@
<!-- Various things involving parens and tuples -->

* `()`: empty tuple (*a.k.a.* unit), both literal and type.
* `!`: empty type (*a.k.a.* unit), both literal and type.
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I think this should be something other than "unit".

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petrochenkov commented Aug 4, 2016 •
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rust-lang/rfcs#1216 doesn't contain !-expressions.
"* !: empty type" seems to be the only change in this PR that needs to stay.

@dns2utf8 dns2utf8 force-pushed the doc_never_expression branch from 85b0966 to 0ff8841 Compare August 4, 2016 13:18
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dns2utf8 commented Aug 4, 2016

Good point. Changed it

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Seems OK. Do we want to wait for the ! implementation to land?

@nikomatsakis
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Also, we might want to change the grammar for fn items, which probably specifies ! explicitly.

@dns2utf8
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dns2utf8 commented Aug 5, 2016 •
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Currently it has a special entry with a link:
https://github.com/rust-lang/rust/blame/master/src/doc/book/syntax-index.md#L64

Since it is a very special case, what would you change?

@canndrew
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canndrew commented Aug 9, 2016

I think there's some confusion here. ! is only a type, not a literal or an expression. You can't write let x = !; for example.

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@dns2utf8

Since it is a very special case, what would you change?

I would remove the -> ! business and just have an entry for ! itself, which is a type.

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Also ! should probably be referred to as "never type" instead of "empty type" if that's the nomenclature we've decided to go with.

@dns2utf8 dns2utf8 force-pushed the doc_never_expression branch from 0ff8841 to 43b98f7 Compare August 15, 2016 09:23
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I would leave the empty word in the doc because comming from type theory/haskell, I would search for empty type

canndrew
canndrew reviewed Aug 15, 2016
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src/doc/grammar.md
### Never expressions

```antlr
never_expr : "!" ;
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This still isn't right. ! isn't an expression, just a type (although the sections for primitive types is nothing but FIXMEs at the moment).

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bors commented Aug 18, 2016

☔ The latest upstream changes (presumably #35769) made this pull request unmergeable. Please resolve the merge conflicts.

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I agree with @canndrew's edits, though if the type is called never -- isn't it? I forget -- let's just call it that.

@dns2utf8 dns2utf8 force-pushed the doc_never_expression branch 4 times, most recently from 0929661 to 2632691 Compare August 20, 2016 20:03
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dns2utf8 commented Aug 20, 2016 •
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I added the word "always" and capitalized the never to prevent the missreading @apasel422 mentioned, but I am not sure if it enhances the readability over all.

I agree with @nikomatsakis, it is no longer a special case but I kept the reference to the Diverging Functions

@dns2utf8 dns2utf8 force-pushed the doc_never_expression branch from 2632691 to d9bd4d5 Compare August 20, 2016 20:13
@dns2utf8 dns2utf8 changed the title Add docs for "!" Never type/expression (rfc 1216) Add docs for "!" Never type (rfc 1216) Aug 21, 2016
nikomatsakis
nikomatsakis reviewed Aug 22, 2016
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src/doc/grammar.md
@@ -764,6 +764,13 @@ bound-list := bound | bound '+' bound-list
bound := path | lifetime
```

### Never type
An empty type
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Better, though I feel like we could say a lot more here. :) For example, "A type representing the result of a function which never returns -- for example because it panics or goes into an infinite loop."

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Well, this has been inactive for a while. I'm going to just merge it since it seems like an improvement, even if I think we could expand the text.

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@bors r+ rollup

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bors commented Sep 28, 2016

📌 Commit d9bd4d5 has been approved by nikomatsakis

@sophiajt sophiajt mentioned this pull request Sep 29, 2016
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sophiajt pushed a commit to sophiajt/rust that referenced this pull request Sep 29, 2016
Rollup merge of rust-lang#35286 - dns2utf8:doc_never_expression, r=ni…
83c54dc 
…komatsakis

Add docs for "!" Never type (rfc 1216)

Pull Request: rust-lang/rfcs#1216
Tracking Issue: rust-lang#35121
bors added a commit that referenced this pull request Sep 29, 2016
@bors
Auto merge of #36818 - jonathandturner:rollup, r=jonathandturner
91f34c0 
Rollup of 12 pull requests

- Successful merges: #35286, #35892, #36460, #36704, #36741, #36760, #36787, #36789, #36794, #36803, #36811, #36813
- Failed merges:
@bors bors merged commit d9bd4d5 into rust-lang:master Sep 29, 2016
@dns2utf8 dns2utf8 deleted the doc_never_expression branch September 29, 2016 11:54
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@dns2utf8 @rust-highfive @petrochenkov @nikomatsakis @canndrew @bors @apasel422 @steveklabnik