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Improve the readability of List<T>. #91617

Merged
merged 1 commit into from
Dec 11, 2021
Merged

Improve the readability of List<T>. #91617

merged 1 commit into from
Dec 11, 2021

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nnethercote
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This commit does the following.

  • Expands on some of the things already mentioned in comments.
  • Describes the uniqueness assumption, which is critical but wasn't
    mentioned at all.
  • Rewrites empty() into a clearer form, as provided by Daniel
    Henry-Mantilla on Zulip.
  • Reorders things slightly so that more important things
    are higher up, and incidental things are lower down, which makes
    reading the code easier.

r? @lcnr

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Dec 7, 2021
danielhenrymantilla
danielhenrymantilla approved these changes Dec 7, 2021
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@danielhenrymantilla danielhenrymantilla left a comment •
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Nice, I like very much the fact that it points out that interning is (expected) to be provided at an outer layer, even though this type expects such semantics 👌

compiler/rustc_middle/src/ty/list.rs
data: [T; 0],

opaque: OpaqueListContents,
}
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To expand on what I mentioned on Zulip, note here that data and opaque are deeply intertwined; having them laid out in such a bare fashion is thus an itsy bit error-prone. That is, compare the current definition, even with your great comments added to it, to:

#[repr(C)]
pub struct List<T> {
    len: usize,

    /// `len` elements are expected to be present.
    data: ThinDst<[T]>,
}

/// Const-assert that a pointer to a `List<T>` is thin.
const _: () = {
    let _ = ::core::mem::transmute::<&List<u8>, usize>;
};

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Are you happy with this part of the code as is, or are you suggesting that I change it to what's in the Playground link?

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I can't claim which one is better in a vacuum: I like my suggestion since it reads quite well at the level of the definition of List<T>, but now it's the definition of ThinDst which may seem a bit too "messy" for compiler code. So just let it be, unless other people were to chime in in defense of the ThinDst helper

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@nnethercote nnethercote force-pushed the improve-List-readability branch from b7dbdb6 to a1628a0 Compare December 7, 2021 21:46
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Thanks for the good comments, I have addressed them and updated the code.

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@nnethercote nnethercote force-pushed the improve-List-readability branch from a1628a0 to e73ce93 Compare December 7, 2021 22:48
lcnr
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some additional small nits, deal with them as you like.

after that r=me

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@nnethercote
Improve the readability of List<T>.
769a707 
This commit does the following.
- Expands on some of the things already mentioned in comments.
- Describes the uniqueness assumption, which is critical but wasn't
  mentioned at all.
- Rewrites `empty()` into a clearer form, as provided by Daniel
  Henry-Mantilla on Zulip.
- Reorders things slightly so that more important things
  are higher up, and incidental things are lower down, which makes
  reading the code easier.
@nnethercote nnethercote force-pushed the improve-List-readability branch from e73ce93 to 769a707 Compare December 9, 2021 04:21
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nnethercote commented Dec 9, 2021 •
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New code is up. Gotta be close to an r+ by now 😀

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lcnr commented Dec 9, 2021

@bors r+

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bors commented Dec 9, 2021

📌 Commit 769a707 has been approved by lcnr

@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 Dec 9, 2021
@apiraino apiraino added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Dec 9, 2021
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Dec 9, 2021
@matthiaskrgr
Rollup merge of rust-lang#91617 - nnethercote:improve-List-readabilit…
d06376e 
…y, r=lcnr

Improve the readability of `List<T>`.

This commit does the following.
- Expands on some of the things already mentioned in comments.
- Describes the uniqueness assumption, which is critical but wasn't
  mentioned at all.
- Rewrites `empty()` into a clearer form, as provided by Daniel
  Henry-Mantilla on Zulip.
- Reorders things slightly so that more important things
  are higher up, and incidental things are lower down, which makes
  reading the code easier.

r? `@lcnr`
@matthiaskrgr matthiaskrgr mentioned this pull request Dec 9, 2021
Closed
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Dec 10, 2021
@matthiaskrgr
Rollup merge of rust-lang#91617 - nnethercote:improve-List-readabilit…
a6a38c2 
…y, r=lcnr

Improve the readability of `List<T>`.

This commit does the following.
- Expands on some of the things already mentioned in comments.
- Describes the uniqueness assumption, which is critical but wasn't
  mentioned at all.
- Rewrites `empty()` into a clearer form, as provided by Daniel
  Henry-Mantilla on Zulip.
- Reorders things slightly so that more important things
  are higher up, and incidental things are lower down, which makes
  reading the code easier.

r? ``@lcnr``
@matthiaskrgr matthiaskrgr mentioned this pull request Dec 10, 2021
Closed
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Dec 11, 2021
@matthiaskrgr
Rollup merge of rust-lang#91617 - nnethercote:improve-List-readabilit…
7dea631 
…y, r=lcnr

Improve the readability of `List<T>`.

This commit does the following.
- Expands on some of the things already mentioned in comments.
- Describes the uniqueness assumption, which is critical but wasn't
  mentioned at all.
- Rewrites `empty()` into a clearer form, as provided by Daniel
  Henry-Mantilla on Zulip.
- Reorders things slightly so that more important things
  are higher up, and incidental things are lower down, which makes
  reading the code easier.

r? ```@lcnr```
@matthiaskrgr matthiaskrgr mentioned this pull request Dec 11, 2021
Closed
@matthiaskrgr matthiaskrgr mentioned this pull request Dec 11, 2021
Merged
bors added a commit to rust-lang-ci/rust that referenced this pull request Dec 11, 2021
@bors
Auto merge of rust-lang#91792 - matthiaskrgr:rollup-2epg7jq, r=matthi…
b8dc6aa 
…askrgr

Rollup of 7 pull requests

Successful merges:

 - rust-lang#91617 (Improve the readability of `List<T>`.)
 - rust-lang#91640 (Simplify collection of in-band lifetimes)
 - rust-lang#91682 (rustdoc: Show type layout for type aliases)
 - rust-lang#91711 (Improve `std::iter::zip` example)
 - rust-lang#91717 (Add deprecation warning for --passes)
 - rust-lang#91718 (give more help in the unaligned_references lint)
 - rust-lang#91782 (Correct since attribute for `is_symlink` feature)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 1de7815 into rust-lang:master Dec 11, 2021
@rustbot rustbot added this to the 1.59.0 milestone Dec 11, 2021
@nnethercote nnethercote mentioned this pull request Feb 4, 2022
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@lcnr lcnr lcnr approved these changes

@danielhenrymantilla danielhenrymantilla danielhenrymantilla approved these changes

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