Implement `TryFrom<char>` for `u8` #84640

ids1024 · 2021-04-28T04:27:30Z

Previously suggested in rust-lang/rfcs#2854.

It makes sense to have this since char implements From<u8>. Likewise u32, u64, and u128 (since #79502) implement From<char>.

rust-highfive · 2021-04-28T04:27:33Z

r? @kennytm

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kennytm · 2021-04-28T19:15:33Z

r? @SimonSapin

SimonSapin · 2021-04-28T19:36:21Z

I would have preferred if we didn’t expose conversions between bytes and Unicode through generic conversion traits that do not make the choice of character encoding visible. However since we already have that same conversion the other way around, at this point that’s not a reason not to add this one.

Still, please expand the doc-comment to discuss encodings like https://doc.rust-lang.org/std/primitive.char.html#impl-From%3Cu8%3E does. In fact that can be mostly copy-pasted, with things like "encode" instead of "decode".

Also please have the docs on the impl rather than only the method. Some rustdoc views fold/hide the latter.

ids1024 · 2021-04-28T20:01:16Z

Updated the doc comment.

I would have preferred if we didn’t expose conversions between bytes and Unicode through generic conversion traits that do not make the choice of character encoding visible. However since we already have that same conversion the other way around, at this point that’s not a reason not to add this one.

Indeed. If From<u8> for char and such didn't already exist, it would be worth considering what function naming would most clearly match the behavior. But too late for that I suppose.

SimonSapin · 2021-04-28T20:06:03Z

@bors r+

bors · 2021-04-28T20:06:04Z

📌 Commit b383d7885ba7bcd0da670e4ba7ac2ec5ad76e618 has been approved by SimonSapin

m-ou-se · 2021-04-28T21:56:37Z

Shouldn't this go through FCP first?

Regardless, the stable version here is set to 1.52.0, which is to be released next week. It should be 1.53 or 1.54 if this were to be merged now.

@bors r-

ids1024 · 2021-04-28T22:40:29Z

Regardless, the stable version here is set to 1.52.0, which is to be released next week. It should be 1.53 or 1.54 if this were to be merged now.

Ah right. Updated that to 1.53.

SimonSapin · 2021-04-29T17:27:21Z

Oh right, I forgot this is insta-stable.

As discussed above, this conversion complements the existing impl From<u8> for char and copies most of its docs regarding the semantics of this "identity" character encoding.

@rfcbot fcp merge

joshtriplett · 2021-04-29T22:17:46Z

Let's try that again and see if rfcbot notices:

@rfcbot merge

rfcbot · 2021-04-29T22:17:48Z

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

Concerns:

duplicated-docs (Implement TryFrom<char> for u8 #84640 (comment))
unique error type (Implement TryFrom<char> for u8 #84640 (comment))

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.

library/core/src/char/convert.rs

jyn514 · 2021-10-03T11:25:07Z

Hm, I guess the issue is that the relative path doesn't work because the docs appear on two pages (u8 and TryFrom).

This should be fixed if you use intra-doc links. Since #87073 rustdoc allows anchors in links to primitives, but you'll have to wait a few weeks for the bootstrap compiler to be bumped.

jyn514 · 2021-10-03T11:26:24Z

Oh right, I forgot I already commented on this PR 🤦

ids1024 · 2021-10-23T03:42:27Z

Updated the error type and the doc link, though that's still not working. Not sure what the schedule for bootstrap compile updates is.

jyn514 · 2021-10-23T05:13:20Z

@ids1024 #90042

ids1024 · 2021-10-27T16:39:31Z

Rebasing now that that PR is merged, CI is passing.

library/core/src/char/mod.rs

m-ou-se · 2021-12-04T17:38:37Z

Sorry for the delay. This looks ready to merge now. Can you update the stabilization version to 1.59.0?

Previously suggested in rust-lang/rfcs#2854. It makes sense to have this since `char` implements `From<u8>`. Likewise `u32`, `u64`, and `u128` (since rust-lang#79502) implement `From<char>`.

m-ou-se · 2022-01-08T01:27:13Z

@bors r+ p=1 rollup

bors · 2022-01-08T01:27:14Z

📌 Commit a02639d has been approved by m-ou-se

Rollup of 8 pull requests Successful merges: - rust-lang#84640 (Implement `TryFrom<char>` for `u8`) - rust-lang#92336 (Remove &self from PrintState::to_string) - rust-lang#92375 (Consolidate checking for msvc when generating debuginfo) - rust-lang#92568 (Add note about non_exhaustive to variant_count) - rust-lang#92600 (Add some missing `#[must_use]` to some `f{32,64}` operations) - rust-lang#92610 (Create CSS class instead of using inline style for search results) - rust-lang#92632 (Implement stabilization of `#[feature(available_parallelism)]`) - rust-lang#92650 (Fix typo in `StableCrateId` docs) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup

bors · 2022-01-08T08:55:40Z

⌛ Testing commit a02639d with merge 84abaf3...

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Implement TryFrom<char> for u8

a02639d

Previously suggested in rust-lang/rfcs#2854. It makes sense to have this since `char` implements `From<u8>`. Likewise `u32`, `u64`, and `u128` (since rust-lang#79502) implement `From<char>`.

ids1024 force-pushed the u8_from_char branch from 92b0ebc to a02639d Compare January 7, 2022 21:09

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-blocked Status: Blocked on something else such as an RFC or other implementation work. labels Jan 8, 2022

ehuss mentioned this pull request Jan 8, 2022

Rollup of 8 pull requests #92664

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bors merged commit 83de77d into rust-lang:master Jan 8, 2022

rustbot added this to the 1.59.0 milestone Jan 8, 2022

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lukas-code mentioned this pull request Dec 13, 2022

ACP: impl TryFrom<char> for u16 rust-lang/libs-team#146

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ebkalderon mentioned this pull request Jul 26, 2023

Impl TryFrom<char> for u8 rust-lang/rfcs#2854

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Implement `TryFrom<char>` for `u8` #84640

Implement `TryFrom<char>` for `u8` #84640

ids1024 commented Apr 28, 2021

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rfcbot commented Apr 29, 2021 •

edited by joshtriplett

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Implement TryFrom<char> for u8 #84640

Implement TryFrom<char> for u8 #84640

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Implement `TryFrom<char>` for `u8` #84640

Implement `TryFrom<char>` for `u8` #84640

rfcbot commented Apr 29, 2021 •

edited by joshtriplett

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