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std: Derive `Default` for `io::Cursor` #60234

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merged 1 commit into from May 10, 2019

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@tesaguri
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commented Apr 24, 2019

I think this change is quite obvious, so made it insta-stable, but I won't insist on that.

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commented Apr 24, 2019

r? @withoutboats

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

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commented Apr 24, 2019

Unfortunately trait impls can't be made unstable, so this can only be landed as an insta-stable impl

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commented Apr 24, 2019

So this would make Cursor::<Vec<u8>>::default() possible, but is that really something one would do? Don't you rather want to wrap an existing Vec, because you want that content?

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commented Apr 24, 2019

I'm dealing with a S: futures::Stream, so the content is not immediately available and I need a placeholder. I could just write Cursor::new(/* ... */) if S::Item were a concrete type (Cursor), but actually that is a type parameter with a trait bound S::Item: bytes::Buf + Default.

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commented Apr 24, 2019

You should be able to use Cursor::new(Default::default()) anywhere Cursor::default() would work.
(not that I think this change shouldn't be made; I'm ambivalent)

@Centril Centril added the relnotes label Apr 25, 2019

@Centril Centril added this to the 1.36 milestone Apr 25, 2019

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commented Apr 28, 2019

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commented Apr 29, 2019

I think this is fine, but just in case anyone has objections...

@rfcbot fcp merge

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commented Apr 29, 2019

Team member @Amanieu 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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commented Apr 29, 2019

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

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commented May 9, 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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commented May 9, 2019

@bors r=Amanieu rollup

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commented May 9, 2019

📌 Commit 902904a has been approved by Amanieu

Centril added a commit to Centril/rust that referenced this pull request May 9, 2019

Rollup merge of rust-lang#60234 - tesaguri:cursor-default, r=Amanieu
std: Derive `Default` for `io::Cursor`

I think this change is quite obvious, so made it insta-stable, but I won't insist on that.

@Centril Centril referenced this pull request May 9, 2019

Merged

Rollup of 8 pull requests #60683

bors added a commit that referenced this pull request May 10, 2019

Auto merge of #60683 - Centril:rollup-p05qh5d, r=Centril
Rollup of 8 pull requests

Successful merges:

 - #59348 (Clean up and add tests for slice drop shims)
 - #60188 (Identify when a stmt could have been parsed as an expr)
 - #60234 (std: Derive `Default` for `io::Cursor`)
 - #60618 (Comment ext::tt::transcribe)
 - #60648 (Skip codegen for one UI test with long file path)
 - #60671 (remove unneeded `extern crate`s from build tools)
 - #60675 (Remove the old await! macro)
 - #60676 (Fix async desugaring providing wrong input to procedural macros.)

Failed merges:

r? @ghost

@bors bors merged commit 902904a into rust-lang:master May 10, 2019

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@tesaguri tesaguri deleted the tesaguri:cursor-default branch May 10, 2019

netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Jul 5, 2019

he
Update rust to version 1.36.0
Pkgsrc changes:
 * NetBSD/sparc64 disabling of "packed" removed ("packed" removed upstream)
 * Adapt src_libstd_build.rs patch, update sed'ing of .cargo-checksum.json

Build verified on NetBSD 8.0/amd64.

Upstream changes:

Version 1.36.0 (2019-07-04)
==========================

Language
--------
- [Non-Lexical Lifetimes are now enabled on the 2015 edition.][59114]
- [The order of traits in trait objects no longer affects the semantics of that
  object.][59445] e.g. `dyn Send + fmt::Debug` is now equivalent to
  `dyn fmt::Debug + Send`, where this was previously not the case.

Libraries
---------
- [`HashMap`'s implementation has been replaced with `hashbrown::HashMap` implem
entation.][58623]
- [`TryFromSliceError` now implements `From<Infallible>`.][60318]
- [`mem::needs_drop` is now available as a const fn.][60364]
- [`alloc::Layout::from_size_align_unchecked` is now available as a const fn.][6
0370]
- [`String` now implements `BorrowMut<str>`.][60404]
- [`io::Cursor` now implements `Default`.][60234]
- [Both `NonNull::{dangling, cast}` are now const fns.][60244]
- [The `alloc` crate is now stable.][59675] `alloc` allows you to use a subset
  of `std` (e.g. `Vec`, `Box`, `Arc`) in `#![no_std]` environments if the
  environment has access to heap memory allocation.
- [`String` now implements `From<&String>`.][59825]
- [You can now pass multiple arguments to the `dbg!` macro.][59826] `dbg!` will
  return a tuple of each argument when there is multiple arguments.
- [`Result::{is_err, is_ok}` are now `#[must_use]` and will produce a warning if
  not used.][59648]

Stabilized APIs
---------------
- [`VecDeque::rotate_left`]
- [`VecDeque::rotate_right`]
- [`Iterator::copied`]
- [`io::IoSlice`]
- [`io::IoSliceMut`]
- [`Read::read_vectored`]
- [`Write::write_vectored`]
- [`str::as_mut_ptr`]
- [`mem::MaybeUninit`]
- [`pointer::align_offset`]
- [`future::Future`]
- [`task::Context`]
- [`task::RawWaker`]
- [`task::RawWakerVTable`]
- [`task::Waker`]
- [`task::Poll`]

Cargo
-----
- [Cargo will now produce an error if you attempt to use the name of a required
dependency as a feature.][cargo/6860]
- [You can now pass the `--offline` flag to run cargo without accessing the netw
ork.][cargo/6934]

You can find further change's in [Cargo's 1.36.0 release notes][cargo-1-36-0].

Clippy
------
There have been numerous additions and fixes to clippy, see [Clippy's 1.36.0 rel
ease notes][clippy-1-36-0] for more details.

Misc
----

Compatibility Notes
-------------------
- [`std::arch::x86::_rdtsc` returns `u64` instead of `i64`][stdsimd/559]
- [`std::arch::x86_64::_mm_shuffle_ps` takes an `i32` instead of `u32` for `mask
`][stdsimd/522]
- With the stabilisation of `mem::MaybeUninit`, `mem::uninitialized` use is no
  longer recommended, and will be deprecated in 1.38.0.

[60318]: rust-lang/rust#60318
[60364]: rust-lang/rust#60364
[60370]: rust-lang/rust#60370
[60404]: rust-lang/rust#60404
[60234]: rust-lang/rust#60234
[60244]: rust-lang/rust#60244
[58623]: rust-lang/rust#58623
[59648]: rust-lang/rust#59648
[59675]: rust-lang/rust#59675
[59825]: rust-lang/rust#59825
[59826]: rust-lang/rust#59826
[59445]: rust-lang/rust#59445
[59114]: rust-lang/rust#59114
[cargo/6860]: rust-lang/cargo#6860
[cargo/6934]: rust-lang/cargo#6934
[`VecDeque::rotate_left`]: https://doc.rust-lang.org/std/collections/struct.VecDeque.html#method.rotate_left
[`VecDeque::rotate_right`]: https://doc.rust-lang.org/std/collections/struct.VecDeque.html#method.rotate_right
[`Iterator::copied`]: https://doc.rust-lang.org/std/iter/trait.Iterator.html#tymethod.copied
[`io::IoSlice`]: https://doc.rust-lang.org/std/io/struct.IoSlice.html
[`io::IoSliceMut`]: https://doc.rust-lang.org/std/io/struct.IoSliceMut.html
[`Read::read_vectored`]: https://doc.rust-lang.org/std/io/trait.Read.html#method.read_vectored
[`Write::write_vectored`]: https://doc.rust-lang.org/std/io/trait.Write.html#method.write_vectored
[`str::as_mut_ptr`]: https://doc.rust-lang.org/std/primitive.str.html#method.as_mut_ptr
[`mem::MaybeUninit`]: https://doc.rust-lang.org/std/mem/union.MaybeUninit.html
[`pointer::align_offset`]: https://doc.rust-lang.org/std/primitive.pointer.html#method.align_offset
[`future::Future`]: https://doc.rust-lang.org/std/future/trait.Future.html
[`task::Context`]: https://doc.rust-lang.org/beta/std/task/struct.Context.html
[`task::RawWaker`]: https://doc.rust-lang.org/beta/std/task/struct.RawWaker.html
[`task::RawWakerVTable`]: https://doc.rust-lang.org/beta/std/task/struct.RawWakerVTable.html
[`task::Waker`]: https://doc.rust-lang.org/beta/std/task/struct.Waker.html
[`task::Poll`]: https://doc.rust-lang.org/beta/std/task/enum.Poll.html
[clippy-1-36-0]: https://github.com/rust-lang/rust-clippy/blob/master/CHANGELOG.md#rust-136
[cargo-1-36-0]: https://github.com/rust-lang/cargo/blob/master/CHANGELOG.md#cargo-136-2019-07-04
[stdsimd/522]: rust-lang/stdarch#522
[stdsimd/559]: rust-lang/stdarch#559
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