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impl From<Cow> for Box, Rc, and Arc #71447

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merged 4 commits into from
May 19, 2020
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@cuviper cuviper commented Apr 22, 2020

These forward Borrowed/Owned values to existing From impls.

  • Box<T> is a fundamental type, so it would be a breaking change to add a blanket impl. Therefore, From<Cow> is only implemented for [T], str, CStr, OsStr, and Path.
  • For Rc<T> and Arc<T>, From<Cow> is implemented for everything that implements From the borrowed and owned types separately.

cuviper added 3 commits April 22, 2020 13:03
These forward `Borrowed`/`Owned` values to existing `Box::from` impls.

- `From<Cow<'_, [T]>> for Box<[T]>`
- `From<Cow<'_, str>> for Box<str>`
- `From<Cow<'_, CStr>> for Box<CStr>`
- `From<Cow<'_, OsStr>> for Box<OsStr>`
- `From<Cow<'_, Path>> for Box<Path>`
These forward `Borrowed`/`Owned` values to existing `From` impls.

    impl<'a, B> From<Cow<'a, B>> for Rc<B>
    where
        B: ToOwned + ?Sized,
        Rc<B>: From<&'a B> + From<B::Owned>,

    impl<'a, B> From<Cow<'a, B>> for Arc<B>
    where
        B: ToOwned + ?Sized,
        Arc<B>: From<&'a B> + From<B::Owned>,
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r? @cramertj

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@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Apr 22, 2020
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Looks good to me.

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pickfire commented May 1, 2020

I will probably create another pull request for Path.

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cuviper commented May 1, 2020

@pickfire What do you mean? I did implement for Box<Path> here.

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pickfire commented May 1, 2020

impl AsRef<Path> for Cow<'_, str> is that possible?

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cuviper commented May 2, 2020

impl AsRef<Path> for Cow<'_, str> is that possible?

Oh, sure, that seems fine. It's tangential to this PR though.

Let's try another reviewer here...

r? @dtolnay

@rust-highfive rust-highfive assigned dtolnay and unassigned cramertj May 2, 2020
@dtolnay dtolnay added the T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. label May 9, 2020
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I think I am on board with all of these. Thanks @cuviper.

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dtolnay commented May 9, 2020

@rust-lang/libs:
@rfcbot fcp merge

impl From<Cow<str>> for Box<str> {...}
impl From<Cow<CStr>> for Box<CStr> {...}
impl From<Cow<OsStr>> for Box<OsStr> {...}
impl From<Cow<Path>> for Box<Path> {...}

impl<T> From<Cow<[T]>> for Box<[T]>
where
    T: Copy,
{...}

impl<'a, B> From<Cow<'a, B>> for Rc<B>
where
    B: ToOwned + ?Sized,
    Rc<B>: From<&'a B> + From<B::Owned>,
{...}

impl<'a, B> From<Cow<'a, B>> for Arc<B>
where
    B: ToOwned + ?Sized,
    Arc<B>: From<&'a B> + From<B::Owned>,
{...}

All of the impls follow the same pattern:

fn from(cow: Cow<...>) -> Self {
    match cow {
        Cow::Borrowed(v) => Self::from(v),
        Cow::Owned(v) => Self::from(v),
    }
}

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rfcbot commented May 9, 2020

Team member @dtolnay 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.

@rfcbot 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 May 9, 2020
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rfcbot commented May 9, 2020

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

@rfcbot rfcbot added final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. and removed proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. labels May 9, 2020
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dtolnay commented May 19, 2020

@bors r+

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bors commented May 19, 2020

📌 Commit 22efd95 has been approved by dtolnay

@bors 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 May 19, 2020
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bors commented May 19, 2020

⌛ Testing commit 22efd95 with merge 914adf0...

@dtolnay dtolnay added the relnotes Marks issues that should be documented in the release notes of the next release. label May 19, 2020
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bors commented May 19, 2020

☀️ Test successful - checks-azure
Approved by: dtolnay
Pushing 914adf0 to master...

@bors bors added the merged-by-bors This PR was explicitly merged by bors. label May 19, 2020
@bors bors merged commit 914adf0 into rust-lang:master May 19, 2020
@rfcbot rfcbot added finished-final-comment-period The final comment period is finished for this PR / Issue. and removed final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. labels May 19, 2020
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jplatte commented May 26, 2020

This should get a relnotes label and milestone of 1.45, no?

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cuviper commented May 26, 2020

@jplatte as a stable library addition, yes, I suppose so.

@dtolnay dtolnay added this to the 1.45 milestone May 26, 2020
@cuviper cuviper deleted the unsized_cow branch May 30, 2020 21:55
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Aug 6, 2020
While here clean up all pkglint warnings.  Changes since 1.44.1:

Version 1.45.2 (2020-08-03)
==========================

* [Fix bindings in tuple struct patterns][74954]
* [Fix track_caller integration with trait objects][74784]

[74954]: rust-lang/rust#74954
[74784]: rust-lang/rust#74784

Version 1.45.1 (2020-07-30)
==========================

* [Fix const propagation with references.][73613]
* [rustfmt accepts rustfmt_skip in cfg_attr again.][73078]
* [Avoid spurious implicit region bound.][74509]
* [Install clippy on x.py install][74457]

[73613]: rust-lang/rust#73613
[73078]: rust-lang/rust#73078
[74509]: rust-lang/rust#74509
[74457]: rust-lang/rust#74457

Version 1.45.0 (2020-07-16)
==========================

Language
--------
- [Out of range float to int conversions using `as` has been defined as a saturating
  conversion.][71269] This was previously undefined behaviour, but you can use the
   `{f64, f32}::to_int_unchecked` methods to continue using the current behaviour, which
   may be desirable in rare performance sensitive situations.
- [`mem::Discriminant<T>` now uses `T`'s discriminant type instead of always
  using `u64`.][70705]
- [Function like procedural macros can now be used in expression, pattern, and  statement
  positions.][68717] This means you can now use a function-like procedural macro
  anywhere you can use a declarative (`macro_rules!`) macro.

Compiler
--------
- [You can now override individual target features through the `target-feature`
  flag.][72094] E.g. `-C target-feature=+avx2 -C target-feature=+fma` is now
  equivalent to `-C target-feature=+avx2,+fma`.
- [Added the `force-unwind-tables` flag.][69984] This option allows
  rustc to always generate unwind tables regardless of panic strategy.
- [Added the `embed-bitcode` flag.][71716] This codegen flag allows rustc
  to include LLVM bitcode into generated `rlib`s (this is on by default).
- [Added the `tiny` value to the `code-model` codegen flag.][72397]
- [Added tier 3 support\* for the `mipsel-sony-psp` target.][72062]
- [Added tier 3 support for the `thumbv7a-uwp-windows-msvc` target.][72133]

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


Libraries
---------
- [`net::{SocketAddr, SocketAddrV4, SocketAddrV6}` now implements `PartialOrd`
  and `Ord`.][72239]
- [`proc_macro::TokenStream` now implements `Default`.][72234]
- [You can now use `char` with
  `ops::{Range, RangeFrom, RangeFull, RangeInclusive, RangeTo}` to iterate over
  a range of codepoints.][72413] E.g.
  you can now write the following;
  ```rust
  for ch in 'a'..='z' {
      print!("{}", ch);
  }
  println!();
  // Prints "abcdefghijklmnopqrstuvwxyz"
  ```
- [`OsString` now implements `FromStr`.][71662]
- [The `saturating_neg` method as been added to all signed integer primitive
  types, and the `saturating_abs` method has been added for all integer
  primitive types.][71886]
- [`Arc<T>`, `Rc<T>` now implement  `From<Cow<'_, T>>`, and `Box` now
  implements `From<Cow>` when `T` is `[T: Copy]`, `str`, `CStr`, `OsStr`,
  or `Path`.][71447]
- [`Box<[T]>` now implements `From<[T; N]>`.][71095]
- [`BitOr` and `BitOrAssign` are implemented for all `NonZero`
  integer types.][69813]
- [The `fetch_min`, and `fetch_max` methods have been added to all atomic
  integer types.][72324]
- [The `fetch_update` method has been added to all atomic integer types.][71843]

Stabilized APIs
---------------
- [`Arc::as_ptr`]
- [`BTreeMap::remove_entry`]
- [`Rc::as_ptr`]
- [`rc::Weak::as_ptr`]
- [`rc::Weak::from_raw`]
- [`rc::Weak::into_raw`]
- [`str::strip_prefix`]
- [`str::strip_suffix`]
- [`sync::Weak::as_ptr`]
- [`sync::Weak::from_raw`]
- [`sync::Weak::into_raw`]
- [`char::UNICODE_VERSION`]
- [`Span::resolved_at`]
- [`Span::located_at`]
- [`Span::mixed_site`]
- [`unix::process::CommandExt::arg0`]

Cargo
-----

Misc
----
- [Rustdoc now supports strikethrough text in Markdown.][71928] E.g.
  `~~outdated information~~` becomes "~~outdated information~~".
- [Added an emoji to Rustdoc's deprecated API message.][72014]

Compatibility Notes
-------------------
- [Trying to self initialize a static value (that is creating a value using
  itself) is unsound and now causes a compile error.][71140]
- [`{f32, f64}::powi` now returns a slightly different value on Windows.][73420]
  This is due to changes in LLVM's intrinsics which `{f32, f64}::powi` uses.
- [Rustdoc's CLI's extra error exit codes have been removed.][71900] These were
  previously undocumented and not intended for public use. Rustdoc still provides
  a non-zero exit code on errors.

Internals Only
--------------
- [Make clippy a git subtree instead of a git submodule][70655]
- [Unify the undo log of all snapshot types][69464]

[73420]: rust-lang/rust#73420
[72324]: rust-lang/rust#72324
[71843]: rust-lang/rust#71843
[71886]: rust-lang/rust#71886
[72234]: rust-lang/rust#72234
[72239]: rust-lang/rust#72239
[72397]: rust-lang/rust#72397
[72413]: rust-lang/rust#72413
[72014]: rust-lang/rust#72014
[72062]: rust-lang/rust#72062
[72094]: rust-lang/rust#72094
[72133]: rust-lang/rust#72133
[71900]: rust-lang/rust#71900
[71928]: rust-lang/rust#71928
[71662]: rust-lang/rust#71662
[71716]: rust-lang/rust#71716
[71447]: rust-lang/rust#71447
[71269]: rust-lang/rust#71269
[71095]: rust-lang/rust#71095
[71140]: rust-lang/rust#71140
[70655]: rust-lang/rust#70655
[70705]: rust-lang/rust#70705
[69984]: rust-lang/rust#69984
[69813]: rust-lang/rust#69813
[69464]: rust-lang/rust#69464
[68717]: rust-lang/rust#68717
[`Arc::as_ptr`]: https://doc.rust-lang.org/stable/std/sync/struct.Arc.html#method.as_ptr
[`BTreeMap::remove_entry`]: https://doc.rust-lang.org/stable/std/collections/struct.BTreeMap.html#method.remove_entry
[`Rc::as_ptr`]: https://doc.rust-lang.org/stable/std/rc/struct.Rc.html#method.as_ptr
[`rc::Weak::as_ptr`]: https://doc.rust-lang.org/stable/std/rc/struct.Weak.html#method.as_ptr
[`rc::Weak::from_raw`]: https://doc.rust-lang.org/stable/std/rc/struct.Weak.html#method.from_raw
[`rc::Weak::into_raw`]: https://doc.rust-lang.org/stable/std/rc/struct.Weak.html#method.into_raw
[`sync::Weak::as_ptr`]: https://doc.rust-lang.org/stable/std/sync/struct.Weak.html#method.as_ptr
[`sync::Weak::from_raw`]: https://doc.rust-lang.org/stable/std/sync/struct.Weak.html#method.from_raw
[`sync::Weak::into_raw`]: https://doc.rust-lang.org/stable/std/sync/struct.Weak.html#method.into_raw
[`str::strip_prefix`]: https://doc.rust-lang.org/stable/std/primitive.str.html#method.strip_prefix
[`str::strip_suffix`]: https://doc.rust-lang.org/stable/std/primitive.str.html#method.strip_suffix
[`char::UNICODE_VERSION`]: https://doc.rust-lang.org/stable/std/char/constant.UNICODE_VERSION.html
[`Span::resolved_at`]: https://doc.rust-lang.org/stable/proc_macro/struct.Span.html#method.resolved_at
[`Span::located_at`]: https://doc.rust-lang.org/stable/proc_macro/struct.Span.html#method.located_at
[`Span::mixed_site`]: https://doc.rust-lang.org/stable/proc_macro/struct.Span.html#method.mixed_site
[`unix::process::CommandExt::arg0`]: https://doc.rust-lang.org/std/os/unix/process/trait.CommandExt.html#tymethod.arg0
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