document const generics #901

lcnr · 2020-11-11T21:36:33Z

blocked on the stabilization of min_const_generics.

shirshak55 · 2020-12-27T11:39:36Z

src/const_eval.md

Co-authored-by: est31 <est31@users.noreply.github.com>

ehuss

Maybe I'm confused, but it seems like the grammar for GenericArgs needs to be updated for expressions?

Also, overall I feel like this is missing a lot of content. There seems to be a large amount of information in the stabilization report that would be good to carry over. There are a lot of details that seem to be missing (like const parameters don't have to be used unlike types and lifetimes). I also see a number of things in the RFC that don't seem to be mentioned.

I appreciate the effort for adding this documentation, but I would like to see a bit more detail if possible.

ehuss · 2020-12-27T16:28:12Z

src/items/generics.md

+> &nbsp;&nbsp; | ( _LifetimeParam_ `,` )<sup>\*</sup> _TypeParams_\
+> &nbsp;&nbsp; | ( _LifetimeParam_ `,` )<sup>\*</sup> ( _TypeParam_ `,` )<sup>\*</sup> _ConstParams_


I believe this grammar is no longer correct (see #785). The order of the parameters doesn't matter syntactically.

You don't have to fix it if you don't want to (although that would be nice), I just wanted to make a note of it.

won't do this in that PR, as I don't know what it's expected to look like now.

src/items/generics.md

ehuss · 2020-12-27T17:34:36Z

src/items/generics.md

+Const parameters may only be be used as standalone arguments inside
+of [types] and [repeat expressions].
+They can be used freely outside of [const contexts].


I find these sentences a little difficult to understand. Can you add more detail, along with some examples?

extended this a bit, it feels weird to go more in depth here as the explanation for types and lifetimes are also fairly short

Co-authored-by: Eric Huss <eric@huss.org>

lcnr · 2020-12-29T20:10:23Z

there is still a lot we could add about const generics or generics in general.

I am not able to spend a lot of time on rust in the near future so I would prefer merging this without adding too much more

ehuss · 2020-12-30T17:16:25Z

src/paths.md

+> _GenericArgsConsts_ :\
+> &nbsp;&nbsp; [_Expression_] (`,` [_Expression_])<sup>\*</sup>


I don't think this is the actual grammar for arguments is it? According to parse_generic_arg I believe it is something like this:

diff --git a/src/paths.md b/src/paths.md index 9126e5b..47a14ee 100644 --- a/src/paths.md +++ b/src/paths.md @@ -70,7 +70,13 @@ mod m { >    [_Type_] (`,` [_Type_])\* > > _GenericArgsConsts_ :\ ->    [_Expression_] (`,` [_Expression_])\* +>    _GenericArgsConst_ (`,` _GenericArgsConst_)\* +> +> _GenericArgsConst_ :\ +>       [_BlockExpression_]\ +>    | [_LiteralExpression_]\ +>    | `-` [_LiteralExpression_]\ +>    | [_SimplePathSegment_] > > _GenericArgsBindings_ :\ >    _GenericArgsBinding_ (`,` _GenericArgsBinding_)\* @@ -375,10 +381,13 @@ mod without { // ::without # fn main() {} ``` +[_BlockExpression_]: expressions/block-expr.md +[_Expression_]: expressions.md [_GenericArgs_]: #paths-in-expressions [_Lifetime_]: trait-bounds.md +[_LiteralExpression_]: expressions/literal-expr.md +[_SimplePathSegment_]: #simple-paths [_Type_]: types.md#type-expressions -[_Expression_]: expressions.md [literal]: expressions/literal-expr.md [item]: items.md [variable]: variables.md

Is that correct?

yeah, that looks right to me

ehuss · 2020-12-30T17:17:00Z

I am not able to spend a lot of time on rust in the near future so I would prefer merging this without adding too much more

No worries, if you can confirm the comment above about the grammar, I can probably merge this and work on extending it.

lcnr · 2020-12-30T17:46:20Z

src/paths.md

@@ -81,6 +89,9 @@ ambiguity with the less-than operator. This is colloquially known as "turbofish"
 Vec::<u8>::with_capacity(1024);
 ```

+Const arguments must be surrounded by braces unless they are a
+[literal] or a single segment path.


in this case this section might not be needed

ehuss

I went ahead and pushed the fix for the grammar. I'll follow up with other PRs.

Update books ## nomicon 2 commits in a5a48441d411f61556b57d762b03d6874afe575d..a8584998eacdea7106a1dfafcbf6c1c06fcdf925 2020-12-06 10:39:41 +0900 to 2021-01-06 12:49:49 -0500 - Update vector code examples - Remove outdated information about `jemalloc` ## reference 13 commits in b278478b766178491a8b6f67afa4bcd6b64d977a..50af691f838937c300b47812d0507c6d88c14f97 2020-12-21 18:18:03 -0800 to 2021-01-12 21:19:20 -0800 - Update grammar for parser unification. (rust-lang/reference#927) - Define constraining an implementation (rust-lang/reference#928) - Document extra behavior of #[no_mangle] (rust-lang/reference#930) - Add a float examle without a `.`. (rust-lang/reference#929) - Add more details about const generics. (rust-lang/reference#921) - Fix footnotes. (rust-lang/reference#926) - Add "Logic errors" as behavior not considered unsafe (rust-lang/reference#919) - Update grammar for order of parameters/arguments. (rust-lang/reference#920) - Fix formatting in the tuple section (rust-lang/reference#923) - document const generics (rust-lang/reference#901) - Update mdbook (rust-lang/reference#918) - linkage.md: update link to FFI section of the Book. (rust-lang/reference#917) - Document array expression with a const. (rust-lang/reference#914) ## book 8 commits in 5bb44f8b5b0aa105c8b22602e9b18800484afa21..ac57a0ddd23d173b26731ccf939f3ba729753275 2020-12-18 20:07:31 -0500 to 2021-01-09 14:18:45 -0500 - Update version of mdbook we're testing with to 0.4.5 (rust-lang/book#2561) - Fix grammar in ch13-01-closures.md (rust-lang/book#2534) - Merge remote-tracking branch 'origin/pr/2527' - Clarify code example ch6.3 (rust-lang/book#2485) - Fix link added in rust-lang/book#2495 to be relative and at the bottom - Merge remote-tracking branch 'origin/pr/2495' - Update output to match the updated poem punctuation - Fix rust-lang/book#2539 - Remove fancy apostrophes from poem for Windows ## rust-by-example 3 commits in 1cce0737d6a7d3ceafb139b4a206861fb1dcb2ab..03e23af01f0b4f83a3a513da280e1ca92587f2ec 2020-12-21 17:36:29 -0300 to 2021-01-09 10:20:28 -0300 - Replace for loop with iteration (rust-lang/rust-by-example#1404) - Update mdbook (rust-lang/rust-by-example#1402) - Add note for match guards to include catch-all (rust-lang/rust-by-example#1401) ## embedded-book 1 commits in ba34b8a968f9531d38c4dc4411d5568b7c076bfe..ceec19e873be87c6ee5666b030c6bb612f889a96 2020-11-17 00:20:43 +0000 to 2021-01-03 13:13:10 +0000 - book.toml: add link to GitHub repo (rust-embedded/book#276)

mention const generics

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ehuss added the S-waiting-on-stabilization Waiting for a stabilization PR to be merged in the main Rust repository label Nov 11, 2020

Havvy mentioned this pull request Dec 27, 2020

stabilize #![feature(min_const_generics)] in 1.51 rust-lang/rust#79135

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lcnr and others added 8 commits December 29, 2020 20:01

Update src/items/generics.md

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Co-authored-by: Eric Huss <eric@huss.org>

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Co-authored-by: Eric Huss <eric@huss.org>

Update src/items/generics.md

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Co-authored-by: Eric Huss <eric@huss.org>

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update generic arg docs

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lcnr commented Dec 30, 2020

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Update _GenericArgsConsts_ grammar.

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ehuss removed the S-waiting-on-stabilization Waiting for a stabilization PR to be merged in the main Rust repository label Jan 6, 2021

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ehuss merged commit c81cd07 into rust-lang:master Jan 6, 2021

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Add more details about const generics. #921

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ehuss mentioned this pull request Jan 13, 2021

Update books rust-lang/rust#80973

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document const generics #901

document const generics #901

lcnr commented Nov 11, 2020

shirshak55 commented Dec 27, 2020

ehuss left a comment

ehuss Dec 27, 2020

lcnr Dec 29, 2020

ehuss Dec 27, 2020

lcnr Dec 29, 2020

lcnr commented Dec 29, 2020

ehuss Dec 30, 2020

lcnr Dec 30, 2020

ehuss commented Dec 30, 2020

lcnr Dec 30, 2020

ehuss left a comment

		>    \| ( _LifetimeParam_ `,` )<sup>\*</sup> _TypeParams_\
		>    \| ( _LifetimeParam_ `,` )<sup>\</sup> ( _TypeParam_ `,` )<sup>\</sup> _ConstParams_

		> _GenericArgsConsts_ :\
		>    [_Expression_] (`,` [_Expression_])<sup>\*</sup>

document const generics #901

document const generics #901

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