Remove trait LengthAtMost32 #74060

kpp · 2020-07-05T13:08:43Z

This is a continuation of #74026 preserving the original burrbull's commit.

I talked to @burrbull, he suggested me to finish his PR.

rust-highfive · 2020-07-05T13:08:46Z

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lcnr · 2020-07-05T13:27:56Z

One thing which concerns me is Default for arrays, which afaik we can't implement using const generics rn
as the current Default impl does not have a T: Default bound for N == 0.

So I fear that we will end up with Default being the only trait which is not implemented for all arrays.

kpp · 2020-07-05T14:07:18Z

I suppose we can have impl<T, const N: usize> ConstDefault for [T; N] with #49147 and https://github.com/Centril/rfcs/blob/rfc/const-default/text/0000-const-default.md

withoutboats · 2020-07-05T14:43:05Z

@rfcbot fcp merge

I propose we merge this, making it so that all traits in std implemented for arrays except Default be implemented for every length of array.

These traits have been implemented on top of const generics for over a year, demonstrating that the implementation is solid and reliable.
We have universal consensus that we want a form of const generics that could support at least all of these impls. There is no concern that we are committing ourselves to a feature we would not be able to support in the long term.
Since we know the implementation is solid and that we are going to stabilize this functionality at some point, we should provide this functionality to users sooner, rather than later.

I also think we should have a discussion about an MVP of const generics which is solid enough that we could stabilize it in the near term, but that's a separate discussion.

rfcbot · 2020-07-05T14:43:06Z

src/test/ui/const-generics/array-impls/into-iter-impls-length-33.rs

ollie27 · 2020-07-05T16:36:56Z

The docs will also need to be updated, for example:

rust/src/libstd/primitive_docs.rs

Lines 463 to 483 in 0cd7ff7

    
           /// Arrays of sizes from 0 to 32 (inclusive) implement the following traits if 
        
           /// the element type allows it: 
        
           /// 
        
           /// - [`Debug`][debug] 
        
           /// - [`IntoIterator`][intoiterator] (implemented for `&[T; N]` and `&mut [T; N]`) 
        
           /// - [`PartialEq`][partialeq], [`PartialOrd`][partialord], [`Eq`][eq], [`Ord`][ord] 
        
           /// - [`Hash`][hash] 
        
           /// - [`AsRef`][asref], [`AsMut`][asmut] 
        
           /// - [`Borrow`][borrow], [`BorrowMut`][borrowmut] 
        
           /// - [`Default`][default] 
        
           /// 
        
           /// This limitation on the size `N` exists because Rust does not yet support 
        
           /// code that is generic over the size of an array type. `[Foo; 3]` and `[Bar; 3]` 
        
           /// are instances of same generic type `[T; 3]`, but `[Foo; 3]` and `[Foo; 5]` are 
        
           /// entirely different types. As a stopgap, trait implementations are 
        
           /// statically generated up to size 32. 
        
           /// 
        
           /// Arrays of *any* size are [`Copy`][copy] if the element type is [`Copy`][copy] 
        
           /// and [`Clone`][clone] if the element type is [`Clone`][clone]. This works 
        
           /// because [`Copy`][copy] and [`Clone`][clone] traits are specially known 
        
           /// to the compiler.

nikomatsakis · 2020-07-06T19:37:40Z

@rfcbot reviewed

rfcbot · 2020-07-06T19:37:43Z

🔔 This is now entering its final comment period, as per the review above. 🔔

bors · 2020-07-26T05:50:44Z

📌 Commit 8fc7d47 has been approved by dtolnay

bors · 2020-07-26T05:51:01Z

⌛ Testing commit 8fc7d47 with merge 461707c...

bors · 2020-07-26T07:38:04Z

☀️ Test successful - checks-actions, checks-azure
Approved by: dtolnay
Pushing 461707c to master...

Pkgsrc changes: * Remove patches now integrated upstream, many related to SunOS / Illumos. * The LLVM fix for powerpc is also now integrated upstream. * Adapt those patches where the source has moved or parts are integrated. * The randomness patches no longer applies, and I could not find where those files went... * Provide a separate bootstrap for NetBSD/powerpc 9.0, since apparently the C++ ABI is different from 8.0. Yes, this appears to be specific to the NetBSD powerpc ports. Upstream changes: Version 1.47.0 (2020-10-08) ========================== Language -------- - [Closures will now warn when not used.][74869] Compiler -------- - [Stabilized the `-C control-flow-guard` codegen option][73893], which enables [Control Flow Guard][1.47.0-cfg] for Windows platforms, and is ignored on other platforms. - [Upgraded to LLVM 11.][73526] - [Added tier 3\* support for the `thumbv4t-none-eabi` target.][74419] - [Upgrade the FreeBSD toolchain to version 11.4][75204] - [`RUST_BACKTRACE`'s output is now more compact.][75048] \* Refer to Rust's [platform support page][forge-platform-support] for more information on Rust's tiered platform support. Libraries --------- - [`CStr` now implements `Index<RangeFrom<usize>>`.][74021] - [Traits in `std`/`core` are now implemented for arrays of any length, not just those of length less than 33.][74060] - [`ops::RangeFull` and `ops::Range` now implement Default.][73197] - [`panic::Location` now implements `Copy`, `Clone`, `Eq`, `Hash`, `Ord`, `PartialEq`, and `PartialOrd`.][73583] Stabilized APIs --------------- - [`Ident::new_raw`] - [`Range::is_empty`] - [`RangeInclusive::is_empty`] - [`Result::as_deref`] - [`Result::as_deref_mut`] - [`Vec::leak`] - [`pointer::offset_from`] - [`f32::TAU`] - [`f64::TAU`] The following previously stable APIs have now been made const. - [The `new` method for all `NonZero` integers.][73858] - [The `checked_add`,`checked_sub`,`checked_mul`,`checked_neg`, `checked_shl`, `checked_shr`, `saturating_add`, `saturating_sub`, and `saturating_mul` methods for all integers.][73858] - [The `checked_abs`, `saturating_abs`, `saturating_neg`, and `signum` for all signed integers.][73858] - [The `is_ascii_alphabetic`, `is_ascii_uppercase`, `is_ascii_lowercase`, `is_ascii_alphanumeric`, `is_ascii_digit`, `is_ascii_hexdigit`, `is_ascii_punctuation`, `is_ascii_graphic`, `is_ascii_whitespace`, and `is_ascii_control` methods for `char` and `u8`.][73858] Cargo ----- - [`build-dependencies` are now built with opt-level 0 by default.][cargo/8500] You can override this by setting the following in your `Cargo.toml`. ```toml [profile.release.build-override] opt-level = 3 ``` - [`cargo-help` will now display man pages for commands rather just the `--help` text.][cargo/8456] - [`cargo-metadata` now emits a `test` field indicating if a target has tests enabled.][cargo/8478] - [`workspace.default-members` now respects `workspace.exclude`.][cargo/8485] - [`cargo-publish` will now use an alternative registry by default if it's the only registry specified in `package.publish`.][cargo/8571] Misc ---- - [Added a help button beside Rustdoc's searchbar that explains rustdoc's type based search.][75366] - [Added the Ayu theme to rustdoc.][71237] Compatibility Notes ------------------- - [Bumped the minimum supported Emscripten version to 1.39.20.][75716] - [Fixed a regression parsing `{} && false` in tail expressions.][74650] - [Added changes to how proc-macros are expanded in `macro_rules!` that should help to preserve more span information.][73084] These changes may cause compiliation errors if your macro was unhygenic or didn't correctly handle `Delimiter::None`. - [Moved support for the CloudABI target to tier 3.][75568] - [`linux-gnu` targets now require minimum kernel 2.6.32 and glibc 2.11.][74163] Internal Only -------- - [Improved default settings for bootstrapping in `x.py`.][73964] You can read details about this change in the ["Changes to `x.py` defaults"](https://blog.rust-lang.org/inside-rust/2020/08/30/changes-to-x-py-defaults.html) post on the Inside Rust blog. - [Added the `rustc-docs` component.][75560] This allows you to install and read the documentation for the compiler internal APIs. (Currently only available for `x86_64-unknown-linux-gnu`.) [1.47.0-cfg]: https://docs.microsoft.com/en-us/windows/win32/secbp/control-flow-guard [76980]: rust-lang/rust#76980 [75048]: rust-lang/rust#75048 [74163]: rust-lang/rust#74163 [71237]: rust-lang/rust#71237 [74869]: rust-lang/rust#74869 [73858]: rust-lang/rust#73858 [75716]: rust-lang/rust#75716 [75908]: rust-lang/rust#75908 [75516]: rust-lang/rust#75516 [75560]: rust-lang/rust#75560 [75568]: rust-lang/rust#75568 [75366]: rust-lang/rust#75366 [75204]: rust-lang/rust#75204 [74650]: rust-lang/rust#74650 [74419]: rust-lang/rust#74419 [73964]: rust-lang/rust#73964 [74021]: rust-lang/rust#74021 [74060]: rust-lang/rust#74060 [73893]: rust-lang/rust#73893 [73526]: rust-lang/rust#73526 [73583]: rust-lang/rust#73583 [73084]: rust-lang/rust#73084 [73197]: rust-lang/rust#73197 [72488]: rust-lang/rust#72488 [cargo/8456]: rust-lang/cargo#8456 [cargo/8478]: rust-lang/cargo#8478 [cargo/8485]: rust-lang/cargo#8485 [cargo/8500]: rust-lang/cargo#8500 [cargo/8571]: rust-lang/cargo#8571 [`Ident::new_raw`]: https://doc.rust-lang.org/nightly/proc_macro/struct.Ident.html#method.new_raw [`Range::is_empty`]: https://doc.rust-lang.org/nightly/std/ops/struct.Range.html#method.is_empty [`RangeInclusive::is_empty`]: https://doc.rust-lang.org/nightly/std/ops/struct.RangeInclusive.html#method.is_empty [`Result::as_deref_mut`]: https://doc.rust-lang.org/nightly/std/result/enum.Result.html#method.as_deref_mut [`Result::as_deref`]: https://doc.rust-lang.org/nightly/std/result/enum.Result.html#method.as_deref [`TypeId::of`]: https://doc.rust-lang.org/nightly/std/any/struct.TypeId.html#method.of [`Vec::leak`]: https://doc.rust-lang.org/nightly/std/vec/struct.Vec.html#method.leak [`f32::TAU`]: https://doc.rust-lang.org/nightly/std/f32/consts/constant.TAU.html [`f64::TAU`]: https://doc.rust-lang.org/nightly/std/f64/consts/constant.TAU.html [`pointer::offset_from`]: https://doc.rust-lang.org/nightly/std/primitive.pointer.html#method.offset_from

This bumps the MSRV to 1.47.0 due to rust#74060[0] [0]: rust-lang/rust#74060

…ater Fixes #1977 as of rust-lang/rust#74060 is available since Rust 1.47 Fixes #2041. Closes #2070.

elichai · 2021-09-14T14:55:48Z

I just want to note that now the "stable since" annotation on this traits is confusing,
I tried using <[u8; 64]>::try_from(slice) on rust 1.36, assuming it would work because it says stable since "1.34", but it's not because removing the "at most 32" didn't change the stable annotation.

SimonSapin · 2021-09-19T10:04:05Z

There isn’t an easy fix for that, unfortunately. There’s now a single impl for all lengths and it can only have a single "stable since" attribute. Just changing it to 1.47 would make it incorrect for lengths up to 32.

SimonSapin · 2021-09-19T10:05:26Z

Though this all could be explained in a doc-comment. I’m sure a PR adding that would be welcome.

…r than 32 elements. Much like rust-lang#74060 did for every other trait. This avoids tools like rust-bindgen having to painfully work around this limitations, sometimes incorrectly like in rust-lang/rust-bindgen#2803

burrbull and others added 3 commits July 4, 2020 13:30

remove LengthAtMost32 on AsRef/Borrow impl for array

7d4a92d

Remove the usage of the LengthAtMost32 trait

eff6206

Remove LengthAtMost32

4ad40a8

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withoutboats added A-macros-2.0 Area: Declarative macros 2.0 (#39412) T-lang Relevant to the language team, which will review and decide on the PR/issue. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. labels Jul 5, 2020

rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Jul 5, 2020

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withoutboats removed A-macros-2.0 Area: Declarative macros 2.0 (#39412) F-const_generics `#![feature(const_generics)]` labels Jul 5, 2020

kpp commented Jul 5, 2020

View reviewed changes

src/test/ui/const-generics/array-impls/into-iter-impls-length-33.rs Outdated Show resolved Hide resolved

Fix copypaste in test into-iter-impls-length-33 (const generic 32 -> 33)

44dd95e

Fix array docs (remove mentions about 0 to 32 where possible)

8fc7d47

joshtriplett added the relnotes Marks issues that should be documented in the release notes of the next release. label Jul 5, 2020

rfcbot added the final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. label Jul 6, 2020

rfcbot removed the proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. label Jul 6, 2020

withoutboats added the F-const_generics `#![feature(const_generics)]` label Jul 6, 2020

tesuji mentioned this pull request Jul 7, 2020

Add IntoIterator impl for arrays by value (for [T; N]) #65819

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bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 26, 2020

bors added the merged-by-bors This PR was explicitly merged by bors. label Jul 26, 2020

bors merged commit 461707c into rust-lang:master Jul 26, 2020

This was referenced Jul 26, 2020

mv std libs to library/ #73265

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Add From<E: Error + Send> for Box<dyn Error + Send> impl #73878

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diagnostics: shorten paths of unique symbols #73996

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kpp deleted the remove_length_at_most_32 branch July 26, 2020 07:57

burrbull mentioned this pull request Jul 26, 2020

Traits discussion teskje/dma-poc#1

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aticu mentioned this pull request Jul 27, 2020

Implementation without unsafe is possible droundy/arrayref#18

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alex mentioned this pull request Aug 9, 2020

Use const generics for array Default impl #61415

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tarcieri mentioned this pull request Aug 12, 2020

[Question] PublicKey as_bytes and from_bytes RustCrypto/elliptic-curves#136

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ordian mentioned this pull request Aug 12, 2020

uint: make const matching work again paritytech/parity-common#421

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KodrAus mentioned this pull request Sep 4, 2020

Implement Index and IndexMut for arrays #74989

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pietroalbini mentioned this pull request Oct 5, 2020

release blog post for Rust 1.47 rust-lang/blog.rust-lang.org#702

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Naive implementation of cartesian_power. rust-itertools/itertools#486

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Xiretza added a commit to Xiretza/ghdl that referenced this pull request Feb 23, 2021

sha1: to_u32x16: take array instead of slice

7c0c7e0

This bumps the MSRV to 1.47.0 due to rust#74060[0] [0]: rust-lang/rust#74060

danielverkamp mentioned this pull request Mar 30, 2021

Import crosvm FDT writer rust-vmm/vm-fdt#1

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ian-p-cooke mentioned this pull request Jul 8, 2021

let Rust derive everything but Default for large arrays in 1.47 and later rust-lang/rust-bindgen#2070

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emilio pushed a commit to rust-lang/rust-bindgen that referenced this pull request Jul 16, 2021

Let Rust derive everything but Default for large arrays in 1.47 and l…

a380678

…ater Fixes #1977 as of rust-lang/rust#74060 is available since Rust 1.47 Fixes #2041. Closes #2070.

cuviper mentioned this pull request Sep 8, 2021

Implement Default for all array sizes #88744

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emilio mentioned this pull request Apr 19, 2024

libstd: Use std::array::from_fn to implement Default for arrays larger than 32 elements. #124163

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Remove trait LengthAtMost32 #74060

Remove trait LengthAtMost32 #74060

kpp commented Jul 5, 2020

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SimonSapin commented Sep 19, 2021

Remove trait LengthAtMost32 #74060

Remove trait LengthAtMost32 #74060

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