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Constify LinkedList new function #63684

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merged 1 commit into from Aug 31, 2019

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GrayJack commented Aug 18, 2019

Change the LinkedList::new() function to become a const fn, allowing the use in constant context.

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rust-highfive commented Aug 18, 2019

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @cramertj (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

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Centril commented Aug 18, 2019

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alexcrichton commented Aug 19, 2019

@GrayJack FWIW could you perhaps elaborate on this PR a little bit? There's nothing in the PR description, nothing else in the commit except the title of the PR, and the change simply deletes one word. While self-explanatory enough it's generally good hygiene to have at least a few words motivating the change instead of just leaving it up to readers to figure out what's going on.

@rfcbot fcp merge

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rfcbot commented Aug 19, 2019

Team member @alexcrichton has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

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rfcbot commented Aug 19, 2019

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

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daboross commented Aug 28, 2019

Just wondering: is the lack of unsafety here why this function can be insta-stable const while Vec::new remains marked const_unstable?

Vec::new was similarly marked const, but it was not marked stable:

rust/src/liballoc/vec.rs

Lines 316 to 317 in c422372

#[rustc_const_unstable(feature = "const_vec_new")]
pub const fn new() -> Vec<T> {

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GrayJack commented Aug 28, 2019

@Centril said that Vec is under is blocked for other reason, but I have no more background to know what blocks it.

If in the end is decided that it should be behind a feature gate, I'll gladly do it

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rfcbot commented Aug 29, 2019

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

The RFC will be merged soon.

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Centril commented Aug 29, 2019

r? @Centril @bors r+ rollup

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bors commented Aug 29, 2019

📌 Commit e0f7305 has been approved by Centril

Centril added a commit to Centril/rust that referenced this pull request Aug 30, 2019
Constify LinkedList new function

Change the `LinkedList::new()` function to become a const fn, allowing the use in constant context.
bors added a commit that referenced this pull request Aug 30, 2019
Rollup of 4 pull requests

Successful merges:

 - #61626 (Get rid of special const intrinsic query in favour of `const_eval`)
 - #63600 (Merge oli-obk mail addresses)
 - #63684 (Constify LinkedList new function)
 - #63982 (When accessing private field of union, do not misidentify it as a struct)

Failed merges:

r? @ghost
Centril added a commit to Centril/rust that referenced this pull request Aug 30, 2019
Constify LinkedList new function

Change the `LinkedList::new()` function to become a const fn, allowing the use in constant context.
bors added a commit that referenced this pull request Aug 30, 2019
Rollup of 7 pull requests

Successful merges:

 - #62957 (Match the loop examples)
 - #63600 (Merge oli-obk mail addresses)
 - #63684 (Constify LinkedList new function)
 - #63847 ([rustdoc] Fix system theme detection)
 - #63999 (Add missing links on AsRef trait)
 - #64014 ( miri: detect too large dynamically sized objects )
 - #64015 (some const-eval test tweaks)

Failed merges:

r? @ghost
@bors bors merged commit e0f7305 into rust-lang:master Aug 31, 2019
4 checks passed
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pr Build #20190818.12 succeeded
Details
pr (Linux mingw-check) Linux mingw-check succeeded
Details
pr (Linux x86_64-gnu-llvm-6.0) Linux x86_64-gnu-llvm-6.0 succeeded
Details
pr (LinuxTools) LinuxTools succeeded
Details
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Nov 11, 2019
Pkgsrc changes:
 * Remove patch which no longer applies (but what about RPATH?)
 * Adapt a few patches to changed files upstream.

Upstream changes:

Version 1.39.0 (2019-11-07)
===========================

Language
--------
- [You can now create `async` functions and blocks with `async fn`,
  `async move {}`, and `async {}` respectively, and you can now call
  `.await` on async expressions.][63209]
- [You can now use certain attributes on function, closure, and function
  pointer parameters.][64010] These attributes include `cfg`, `cfg_attr`,
  `allow`, `warn`, `deny`, `forbid` as well as inert helper attributes used
  by procedural macro attributes applied to items. e.g.
  ```rust
  fn len(
      #[cfg(windows)] slice: &[u16],
      #[cfg(not(windows))] slice: &[u8],
  ) -> usize {
      slice.len()
  }
  ```
- [You can now take shared references to bind-by-move patterns in the
  `if` guards of `match` arms.][63118] e.g.
  ```rust
  fn main() {
      let array: Box<[u8; 4]> = Box::new([1, 2, 3, 4]);

      match array {
          nums
  //      ---- `nums` is bound by move.
              if nums.iter().sum::<u8>() == 10
  //                 ^------ `.iter()` implicitly takes a reference to `nums`.
          => {
              drop(nums);
  //          ----------- Legal as `nums` was bound by move and so we have ownership.
          }
          _ => unreachable!(),
      }
  }
  ```

Compiler
--------
- [Added tier 3\* support for the `i686-unknown-uefi` target.][64334]
- [Added tier 3 support for the `sparc64-unknown-openbsd` target.][63595]
- [rustc will now trim code snippets in diagnostics to fit in your terminal.]
  [63402] **Note** Cargo currently doesn't use this feature. Refer to
  [cargo#7315][cargo/7315] to track this feature's progress.
- [You can now pass `--show-output` argument to test binaries to print the
  output of successful tests.][62600]

\* Refer to Rust's [platform support page][forge-platform-support] for more
information on Rust's tiered platform support.

Libraries
---------
- [`Vec::new` and `String::new` are now `const` functions.][64028]
- [`LinkedList::new` is now a `const` function.][63684]
- [`str::len`, `[T]::len` and `str::as_bytes` are now `const` functions.][63770]
- [The `abs`, `wrapping_abs`, and `overflowing_abs` numeric functions are
  now `const`.][63786]

Stabilized APIs
---------------
- [`Pin::into_inner`]
- [`Instant::checked_duration_since`]
- [`Instant::saturating_duration_since`]

Cargo
-----
- [You can now publish git dependencies if supplied with a `version`.]
  [cargo/7237]
- [The `--all` flag has been renamed to `--workspace`.][cargo/7241] Using
  `--all` is now deprecated.

Misc
----
- [You can now pass `-Clinker` to rustdoc to control the linker used
  for compiling doctests.][63834]

Compatibility Notes
-------------------
- [Code that was previously accepted by the old borrow checker, but rejected by
  the NLL borrow checker is now a hard error in Rust 2018.][63565] This was
  previously a warning, and will also become a hard error in the Rust 2015
  edition in the 1.40.0 release.
- [`rustdoc` now requires `rustc` to be installed and in the same directory to
  run tests.][63827] This should improve performance when running a large
  amount of doctests.
- [The `try!` macro will now issue a deprecation warning.][62672] It is
  recommended to use the `?` operator instead.
- [`asinh(-0.0)` now correctly returns `-0.0`.][63698] Previously this
  returned `0.0`.

[62600]: rust-lang/rust#62600
[62672]: rust-lang/rust#62672
[63118]: rust-lang/rust#63118
[63209]: rust-lang/rust#63209
[63402]: rust-lang/rust#63402
[63565]: rust-lang/rust#63565
[63595]: rust-lang/rust#63595
[63684]: rust-lang/rust#63684
[63698]: rust-lang/rust#63698
[63770]: rust-lang/rust#63770
[63786]: rust-lang/rust#63786
[63827]: rust-lang/rust#63827
[63834]: rust-lang/rust#63834
[63927]: rust-lang/rust#63927
[63933]: rust-lang/rust#63933
[63934]: rust-lang/rust#63934
[63938]: rust-lang/rust#63938
[63940]: rust-lang/rust#63940
[63941]: rust-lang/rust#63941
[63945]: rust-lang/rust#63945
[64010]: rust-lang/rust#64010
[64028]: rust-lang/rust#64028
[64334]: rust-lang/rust#64334
[cargo/7237]: rust-lang/cargo#7237
[cargo/7241]: rust-lang/cargo#7241
[cargo/7315]: rust-lang/cargo#7315
[`Pin::into_inner`]: https://doc.rust-lang.org/std/pin/struct.Pin.html#method.into_inner
[`Instant::checked_duration_since`]: https://doc.rust-lang.org/std/time/struct.Instant.html#method.checked_duration_since
[`Instant::saturating_duration_since`]: https://doc.rust-lang.org/std/time/struct.Instant.html#method.saturating_duration_since
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