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merged 1 commit into from
Aug 4, 2021
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Document lifetime elision for fn types, Fn*, impl #298

merged 1 commit into from
Aug 4, 2021

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@ssbr ssbr commented Aug 4, 2021

Currently, the lifetime elision doc only documents function definitions, but lifetime elision is also allowed in the following other locations:

  • fn types, such as fn(&T)
  • Fn/FnMut/FnOnce, such as Fn(&T)
  • impl headers

To demo this up, I made some type aliases for fn/Fn which you can pass &T as a parameter to (to follow the lifetime rules of the surrounding context), and compared what you get with that instead of using fn/Fn directly, where lifetime elision takes on the rules from fn/Fn/etc.

I also demoed up an impl header that used lifetime elision twice, although the error message in that case is broken (filed rust-lang/rust#87763)

The demo was half for this change description, and half just to make sure I understand Rust -- in particular, I really had to reverse engineer it for impl because I wasn't sure, and it didn't seem to be documented anywhere (at least not here!)

https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=f82b280de4b992f225bc32121f333e96

@ssbr
Document lifetime elision for fn types, Fn*, impl
3abf036 
Currently, the lifetime elision doc only documents function definitions, but lifetime elision is also allowed in the following other locations:

* `fn` types, such as `fn(&T)`
* `Fn`/`FnMut`/`FnOnce`, such as `Fn(&T)`
* `impl` headers

To demo this up, I made some type aliases for `fn`/`Fn` which you can pass `&T` as a parameter to (to follow the lifetime rules of the surrounding context), and compared what you get with that instead of using `fn`/`Fn` directly, where lifetime elision takes on the rules from `fn`/`Fn`/etc.

I also demoed up an `impl` header that used lifetime elision twice, although the error message in that case is broken (filed rust-lang/rust#87763)

The demo was half for this change description, and half just to make sure I understand Rust -- in particular, I really had to reverse engineer it for `impl` because I wasn't sure, and it didn't seem to be documented anywhere (at least not here!)

https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=f82b280de4b992f225bc32121f333e96
@Manishearth Manishearth merged commit 0c7e5bd into rust-lang:master Aug 4, 2021
@ehuss ehuss mentioned this pull request Aug 10, 2021
Merged
JohnTitor added a commit to JohnTitor/rust that referenced this pull request Aug 11, 2021
@JohnTitor
Rollup merge of rust-lang#87925 - ehuss:update-books, r=ehuss
0ae6a9c 
Update books

## nomicon

2 commits in f51734eb5566c826b471977747ea3d7d6915bbe9..0c7e5bd1428e7838252bb57b7f0fbfda4ec82f02
2021-07-23 18:24:35 +0900 to 2021-08-04 10:18:22 -0700
- Document lifetime elision for fn types, Fn*, impl (rust-lang/nomicon#298)
- Remove unnecessary `extern crate`s (rust-lang/nomicon#297)

## reference

3 commits in 3b7be075af5d6e402a18efff672a8a265b4596fd..4884fe45c14f8b22121760fb117181bb4da8dfe0
2021-07-26 13:20:11 -0700 to 2021-07-28 21:31:28 -0700
- Mention "function item type to `fn pointer`" coercion (rust-lang/reference#1079)
- example for bindings after at (rust-lang/reference#1027)
- array-expr.md: fix typo; 'polish' sentence (rust-lang/reference#1080)

## book

10 commits in a07036f864b37896b31eb996cd7aedb489f69a1f..7e49659102f0977d9142190e1ba23345c0f00eb1
2021-07-26 20:19:46 -0400 to 2021-08-03 21:41:35 -0400
- Make explicit that enum variant construction is a function
- Clarify why None means we have to annotate the type
- Make the convert quotes script able to do one chapter
- Snapshot of chapter 5
-  (rust-lang/book#2811)
-  (rust-lang/book#2809)
- Ugh quote script, that's not right
- Introduce the dbg macro. Connects to rust-lang/book#1658
- Add an example of declaring and instantiating unit-like structs. Fixes rust-lang/book#2442.
- Remove authors field from all the manifests (rust-lang/book#2805)

## rustc-dev-guide

5 commits in 09343d6..c4644b4
2021-07-26 00:37:28 +0200 to 2021-08-10 20:41:44 +0900
- Remove a dead link in `new-target.md` + other nits (rust-lang/rustc-dev-guide#1186)
- Add description of -opt-bisect-limit LLVM option (rust-lang/rustc-dev-guide#1182)
- Fixed team responsible for stabilization (rust-lang/rustc-dev-guide#1181)
- Add S-Inactive PRs as another source of things contributors could work on (rust-lang/rustc-dev-guide#1177)
- git.md: Fix No-Merge Policy link

## embedded-book

1 commits in 09986cd352404eb4659db44613b27cac9aa652fc..4f9fcaa30d11ba52b641e6fd5206536d65838af9
2021-07-18 19:26:46 +0000 to 2021-08-06 17:43:12 +0000
- Fix typo in 'Memory Mapped Registers'  (rust-embedded/book#298)
JohnTitor added a commit to JohnTitor/rust that referenced this pull request Aug 11, 2021
@JohnTitor
Rollup merge of rust-lang#87925 - ehuss:update-books, r=ehuss
a290246 
Update books

## nomicon

2 commits in f51734eb5566c826b471977747ea3d7d6915bbe9..0c7e5bd1428e7838252bb57b7f0fbfda4ec82f02
2021-07-23 18:24:35 +0900 to 2021-08-04 10:18:22 -0700
- Document lifetime elision for fn types, Fn*, impl (rust-lang/nomicon#298)
- Remove unnecessary `extern crate`s (rust-lang/nomicon#297)

## reference

3 commits in 3b7be075af5d6e402a18efff672a8a265b4596fd..4884fe45c14f8b22121760fb117181bb4da8dfe0
2021-07-26 13:20:11 -0700 to 2021-07-28 21:31:28 -0700
- Mention "function item type to `fn pointer`" coercion (rust-lang/reference#1079)
- example for bindings after at (rust-lang/reference#1027)
- array-expr.md: fix typo; 'polish' sentence (rust-lang/reference#1080)

## book

10 commits in a07036f864b37896b31eb996cd7aedb489f69a1f..7e49659102f0977d9142190e1ba23345c0f00eb1
2021-07-26 20:19:46 -0400 to 2021-08-03 21:41:35 -0400
- Make explicit that enum variant construction is a function
- Clarify why None means we have to annotate the type
- Make the convert quotes script able to do one chapter
- Snapshot of chapter 5
-  (rust-lang/book#2811)
-  (rust-lang/book#2809)
- Ugh quote script, that's not right
- Introduce the dbg macro. Connects to rust-lang/book#1658
- Add an example of declaring and instantiating unit-like structs. Fixes rust-lang/book#2442.
- Remove authors field from all the manifests (rust-lang/book#2805)

## rustc-dev-guide

5 commits in 09343d6..c4644b4
2021-07-26 00:37:28 +0200 to 2021-08-10 20:41:44 +0900
- Remove a dead link in `new-target.md` + other nits (rust-lang/rustc-dev-guide#1186)
- Add description of -opt-bisect-limit LLVM option (rust-lang/rustc-dev-guide#1182)
- Fixed team responsible for stabilization (rust-lang/rustc-dev-guide#1181)
- Add S-Inactive PRs as another source of things contributors could work on (rust-lang/rustc-dev-guide#1177)
- git.md: Fix No-Merge Policy link

## embedded-book

1 commits in 09986cd352404eb4659db44613b27cac9aa652fc..4f9fcaa30d11ba52b641e6fd5206536d65838af9
2021-07-18 19:26:46 +0000 to 2021-08-06 17:43:12 +0000
- Fix typo in 'Memory Mapped Registers'  (rust-embedded/book#298)
JohnTitor added a commit to JohnTitor/rust that referenced this pull request Aug 12, 2021
@JohnTitor
Rollup merge of rust-lang#87925 - ehuss:update-books, r=ehuss
9775e88 
Update books

## nomicon

2 commits in f51734eb5566c826b471977747ea3d7d6915bbe9..0c7e5bd1428e7838252bb57b7f0fbfda4ec82f02
2021-07-23 18:24:35 +0900 to 2021-08-04 10:18:22 -0700
- Document lifetime elision for fn types, Fn*, impl (rust-lang/nomicon#298)
- Remove unnecessary `extern crate`s (rust-lang/nomicon#297)

## reference

3 commits in 3b7be075af5d6e402a18efff672a8a265b4596fd..4884fe45c14f8b22121760fb117181bb4da8dfe0
2021-07-26 13:20:11 -0700 to 2021-07-28 21:31:28 -0700
- Mention "function item type to `fn pointer`" coercion (rust-lang/reference#1079)
- example for bindings after at (rust-lang/reference#1027)
- array-expr.md: fix typo; 'polish' sentence (rust-lang/reference#1080)

## book

10 commits in a07036f864b37896b31eb996cd7aedb489f69a1f..7e49659102f0977d9142190e1ba23345c0f00eb1
2021-07-26 20:19:46 -0400 to 2021-08-03 21:41:35 -0400
- Make explicit that enum variant construction is a function
- Clarify why None means we have to annotate the type
- Make the convert quotes script able to do one chapter
- Snapshot of chapter 5
-  (rust-lang/book#2811)
-  (rust-lang/book#2809)
- Ugh quote script, that's not right
- Introduce the dbg macro. Connects to rust-lang/book#1658
- Add an example of declaring and instantiating unit-like structs. Fixes rust-lang/book#2442.
- Remove authors field from all the manifests (rust-lang/book#2805)

## rustc-dev-guide

5 commits in 09343d6..c4644b4
2021-07-26 00:37:28 +0200 to 2021-08-10 20:41:44 +0900
- Remove a dead link in `new-target.md` + other nits (rust-lang/rustc-dev-guide#1186)
- Add description of -opt-bisect-limit LLVM option (rust-lang/rustc-dev-guide#1182)
- Fixed team responsible for stabilization (rust-lang/rustc-dev-guide#1181)
- Add S-Inactive PRs as another source of things contributors could work on (rust-lang/rustc-dev-guide#1177)
- git.md: Fix No-Merge Policy link

## embedded-book

1 commits in 09986cd352404eb4659db44613b27cac9aa652fc..4f9fcaa30d11ba52b641e6fd5206536d65838af9
2021-07-18 19:26:46 +0000 to 2021-08-06 17:43:12 +0000
- Fix typo in 'Memory Mapped Registers'  (rust-embedded/book#298)
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@Manishearth Manishearth Manishearth approved these changes

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@ssbr @Manishearth