impl From<char> for String #73466

matthiaskrgr · 2020-06-18T03:03:48Z

This allows us to write

fn char_to_string() -> String {
    'a'.into()
}

which was not possible before.

This allows us to write fn char_to_string() -> String { 'a'.into() } which was not possible before.

rust-highfive · 2020-06-18T03:03:51Z

r? @sfackler

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

matthiaskrgr · 2020-06-18T03:04:32Z

I would like to add

fn char_to_string() -> String {
'a'.into()
}

as a test, what is the best place to do so?

matthiaskrgr · 2020-06-18T09:15:08Z

I guess this can go into src/liballoc/tests/string.rs

tesuji · 2020-06-18T10:56:50Z

Does doctest work?

Mark-Simulacrum · 2020-06-18T11:02:32Z

r? @dtolnay for FCP, code changes look good to me.

dtolnay · 2020-06-18T17:13:36Z

@rust-lang/libs:
@rfcbot fcp merge

impl From<char> for String

rfcbot · 2020-06-18T17:13:37Z

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.

sfackler · 2020-06-18T23:31:33Z

It appears that this is the first From<T> for String impl for types other than String, str, and references of those. What is the plan moving forward for these - should every type implementing Display also implement a From conversion?

Mark-Simulacrum · 2020-06-19T00:40:00Z

IMO, char makes sense as it has "string literal" like feeling, but I wouldn't go farther than that personally without good reason.

@matthiaskrgr can you say more about your use case for this?

hellow554 · 2020-06-19T08:08:08Z

I can't find the post, but either on github or on urlo this proposal was denied, because it would allocate memory out of the sudden. And IMHO this is true. It is not obvious that a small into (or a ?, which performs into automatically) will allocate memory behind the scenes.
I'm somewhat against this‽

matthiaskrgr · 2020-06-19T08:38:32Z

can you say more about your use case for this?

When I investigated #73462 I found it strange that I could
"a".into() but not 'a'.into() for a fn conv_to_string() -> String

withoutboats · 2020-06-19T09:11:03Z

I can't find the post, but either on github or on urlo this proposal was denied, because it would allocate memory out of the sudden. And IMHO this is true. It is not obvious that a small into (or a ?, which performs into automatically) will allocate memory behind the scenes.

So will most of the other conversions into String, such as &str to String. There's no expectation that Into<String> does not allocate.

rfcbot · 2020-06-19T09:11:07Z

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

dtolnay · 2020-06-30T18:47:21Z

@bors r

bors · 2020-06-30T18:47:23Z

📌 Commit 2cde493 has been approved by dtolnay

…olnay impl From<char> for String This allows us to write ````rust fn char_to_string() -> String { 'a'.into() } ```` which was not possible before.

pickfire · 2020-07-01T02:56:36Z

Will there also be?

impl From<char> for &str

dtolnay · 2020-07-01T03:17:01Z

No; that impl would require the binary to contain a 4 MB table containing the utf8 encoding of every possible char in order for it to return a reference into.

…olnay impl From<char> for String This allows us to write ````rust fn char_to_string() -> String { 'a'.into() } ```` which was not possible before.

@ghost

…arth Rollup of 17 pull requests Successful merges: - rust-lang#72071 (Added detailed error code explanation for issue E0687 in Rust compiler.) - rust-lang#72369 (Bring net/parser.rs up to modern up to date with modern rust patterns) - rust-lang#72445 (Stabilize `#[track_caller]`.) - rust-lang#73466 (impl From<char> for String) - rust-lang#73548 (remove rustdoc warnings) - rust-lang#73649 (Fix sentence structure) - rust-lang#73678 (Update Box::from_raw example to generalize better) - rust-lang#73705 (stop taking references in Relate) - rust-lang#73716 (Document the static keyword) - rust-lang#73752 (Remap Windows ERROR_INVALID_PARAMETER to ErrorKind::InvalidInput from Other) - rust-lang#73776 (Move terminator to new module) - rust-lang#73778 (Make `likely` and `unlikely` const, gated by feature `const_unlikely`) - rust-lang#73805 (Document the type keyword) - rust-lang#73806 (Use an 'approximate' universal upper bound when reporting region errors) - rust-lang#73828 (Fix wording for anonymous parameter name help) - rust-lang#73846 (Fix comma in debug_assert! docs) - rust-lang#73847 (Edit cursor.prev() method docs in lexer) Failed merges: r? @ghost

according to various people on tech-pkg@, there are no problems with the Firefox build Version 1.46.0 (2020-08-27) ========================== Language -------- - [`if`, `match`, and `loop` expressions can now be used in const functions.][72437] - [Additionally you are now also able to coerce and cast to slices (`&[T]`) in const functions.][73862] - [The `#[track_caller]` attribute can now be added to functions to use the function's caller's location information for panic messages.][72445] - [Recursively indexing into tuples no longer needs parentheses.][71322] E.g. `x.0.0` over `(x.0).0`. - [`mem::transmute` can now be used in static and constants.][72920] **Note** You currently can't use `mem::transmute` in constant functions. Compiler -------- - [You can now use the `cdylib` target on Apple iOS and tvOS platforms.][73516] - [Enabled static "Position Independent Executables" by default for `x86_64-unknown-linux-musl`.][70740] Libraries --------- - [`mem::forget` is now a `const fn`.][73887] - [`String` now implements `From<char>`.][73466] - [The `leading_ones`, and `trailing_ones` methods have been stabilised for all integer types.][73032] - [`vec::IntoIter<T>` now implements `AsRef<[T]>`.][72583] - [All non-zero integer types (`NonZeroU8`) now implement `TryFrom` for their zero-able equivalent (e.g. `TryFrom<u8>`).][72717] - [`&[T]` and `&mut [T]` now implement `PartialEq<Vec<T>>`.][71660] - [`(String, u16)` now implements `ToSocketAddrs`.][73007] - [`vec::Drain<'_, T>` now implements `AsRef<[T]>`.][72584] Stabilized APIs --------------- - [`Option::zip`] - [`vec::Drain::as_slice`] Cargo ----- Added a number of new environment variables that are now available when compiling your crate. - [`CARGO_BIN_NAME` and `CARGO_CRATE_NAME`][cargo/8270] Providing the name of the specific binary being compiled and the name of the crate. - [`CARGO_PKG_LICENSE`][cargo/8325] The license from the manifest of the package. - [`CARGO_PKG_LICENSE_FILE`][cargo/8387] The path to the license file. Compatibility Notes ------------------- - [The target configuration option `abi_blacklist` has been renamed to `unsupported_abis`.][74150] The old name will still continue to work. - [Rustc will now warn if you cast a C-like enum that implements `Drop`.][72331] This was previously accepted but will become a hard error in a future release. - [Rustc will fail to compile if you have a struct with `#[repr(i128)]` or `#[repr(u128)]`.][74109] This representation is currently only allowed on `enum`s. - [Tokens passed to `macro_rules!` are now always captured.][73293] This helps ensure that spans have the correct information, and may cause breakage if you were relying on receiving spans with dummy information. - [The InnoSetup installer for Windows is no longer available.][72569] This was a legacy installer that was replaced by a MSI installer a few years ago but was still being built. - [`{f32, f64}::asinh` now returns the correct values for negative numbers.][72486] - [Rustc will no longer accept overlapping trait implementations that only differ in how the lifetime was bound.][72493] - [Rustc now correctly relates the lifetime of an existential associated type.][71896] This fixes some edge cases where `rustc` would erroneously allow you to pass a shorter lifetime than expected. - [Rustc now dynamically links to `libz` (also called `zlib`) on Linux.][74420] The library will need to be installed for `rustc` to work, even though we expect it to be already available on most systems. - [Tests annotated with `#[should_panic]` are broken on ARMv7 while running under QEMU.][74820] - [Pretty printing of some tokens in procedural macros changed.][75453] The exact output returned by rustc's pretty printing is an unstable implementation detail: we recommend any macro relying on it to switch to a more robust parsing system. [75453]: rust-lang/rust#75453 [74820]: rust-lang/rust#74820 [74420]: rust-lang/rust#74420 [74109]: rust-lang/rust#74109 [74150]: rust-lang/rust#74150 [73862]: rust-lang/rust#73862 [73887]: rust-lang/rust#73887 [73466]: rust-lang/rust#73466 [73516]: rust-lang/rust#73516 [73293]: rust-lang/rust#73293 [73007]: rust-lang/rust#73007 [73032]: rust-lang/rust#73032 [72920]: rust-lang/rust#72920 [72569]: rust-lang/rust#72569 [72583]: rust-lang/rust#72583 [72584]: rust-lang/rust#72584 [72717]: rust-lang/rust#72717 [72437]: rust-lang/rust#72437 [72445]: rust-lang/rust#72445 [72486]: rust-lang/rust#72486 [72493]: rust-lang/rust#72493 [72331]: rust-lang/rust#72331 [71896]: rust-lang/rust#71896 [71660]: rust-lang/rust#71660 [71322]: rust-lang/rust#71322 [70740]: rust-lang/rust#70740 [cargo/8270]: rust-lang/cargo#8270 [cargo/8325]: rust-lang/cargo#8325 [cargo/8387]: rust-lang/cargo#8387 [`Option::zip`]: https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.zip [`vec::Drain::as_slice`]: https://doc.rust-lang.org/stable/std/vec/struct.Drain.html#method.as_slice

Pkgsrc changes: * Portability patches for Illumos have been intregrated upstream, so are no longer needed in pkgsrc. * Adjust one other patch, and update vendor/libc cargo checksum. Upstream changes: Version 1.46.0 (2020-08-27) ========================== Language -------- - [`if`, `match`, and `loop` expressions can now be used in const functions.] [72437] - [Additionally you are now also able to coerce and cast to slices (`&[T]`) in const functions.][73862] - [The `#[track_caller]` attribute can now be added to functions to use the function's caller's location information for panic messages.][72445] - [Recursively indexing into tuples no longer needs parentheses.][71322] E.g. `x.0.0` over `(x.0).0`. - [`mem::transmute` can now be used in static and constants.][72920] **Note** You currently can't use `mem::transmute` in constant functions. Compiler -------- - [You can now use the `cdylib` target on Apple iOS and tvOS platforms.][73516] - [Enabled static "Position Independent Executables" by default for `x86_64-unknown-linux-musl`.][70740] Libraries --------- - [`mem::forget` is now a `const fn`.][73887] - [`String` now implements `From<char>`.][73466] - [The `leading_ones`, and `trailing_ones` methods have been stabilised for all integer types.][73032] - [`vec::IntoIter<T>` now implements `AsRef<[T]>`.][72583] - [All non-zero integer types (`NonZeroU8`) now implement `TryFrom` for their zero-able equivalent (e.g. `TryFrom<u8>`).][72717] - [`&[T]` and `&mut [T]` now implement `PartialEq<Vec<T>>`.][71660] - [`(String, u16)` now implements `ToSocketAddrs`.][73007] - [`vec::Drain<'_, T>` now implements `AsRef<[T]>`.][72584] Stabilized APIs --------------- - [`Option::zip`] - [`vec::Drain::as_slice`] Cargo ----- Added a number of new environment variables that are now available when compiling your crate. - [`CARGO_BIN_NAME` and `CARGO_CRATE_NAME`][cargo/8270] Providing the name of the specific binary being compiled and the name of the crate. - [`CARGO_PKG_LICENSE`][cargo/8325] The license from the manifest of the package. - [`CARGO_PKG_LICENSE_FILE`][cargo/8387] The path to the license file. Compatibility Notes ------------------- - [The target configuration option `abi_blacklist` has been renamed to `unsupported_abis`.][74150] The old name will still continue to work. - [Rustc will now warn if you have a C-like enum that implements `Drop`.][72331] This was previously accepted but will become a hard error in a future release. - [Rustc will fail to compile if you have a struct with `#[repr(i128)]` or `#[repr(u128)]`.][74109] This representation is currently only allowed on `enum`s. - [Tokens passed to `macro_rules!` are now always captured.][73293] This helps ensure that spans have the correct information, and may cause breakage if you were relying on receiving spans with dummy information. - [The InnoSetup installer for Windows is no longer available.][72569] This was a legacy installer that was replaced by a MSI installer a few years ago but was still being built. - [`{f32, f64}::asinh` now returns the correct values for negative numbers.] [72486] - [Rustc will no longer accept overlapping trait implementations that only differ in how the lifetime was bound.][72493] - [Rustc now correctly relates the lifetime of an existential associated type.][71896] This fixes some edge cases where `rustc` would erroneously allow you to pass a shorter lifetime than expected. - [Rustc now dynamically links to `libz` (also called `zlib`) on Linux.][74420] The library will need to be installed for `rustc` to work, even though we expect it to be already available on most systems. - [Tests annotated with `#[should_panic]` are broken on ARMv7 while running under QEMU.][74820] - [Pretty printing of some tokens in procedural macros changed.][75453] The exact output returned by rustc's pretty printing is an unstable implementation detail: we recommend any macro relying on it to switch to a more robust parsing system. [75453]: rust-lang/rust#75453 [74820]: rust-lang/rust#74820 [74420]: rust-lang/rust#74420 [74109]: rust-lang/rust#74109 [74150]: rust-lang/rust#74150 [73862]: rust-lang/rust#73862 [73887]: rust-lang/rust#73887 [73466]: rust-lang/rust#73466 [73516]: rust-lang/rust#73516 [73293]: rust-lang/rust#73293 [73007]: rust-lang/rust#73007 [73032]: rust-lang/rust#73032 [72920]: rust-lang/rust#72920 [72569]: rust-lang/rust#72569 [72583]: rust-lang/rust#72583 [72584]: rust-lang/rust#72584 [72717]: rust-lang/rust#72717 [72437]: rust-lang/rust#72437 [72445]: rust-lang/rust#72445 [72486]: rust-lang/rust#72486 [72493]: rust-lang/rust#72493 [72331]: rust-lang/rust#72331 [71896]: rust-lang/rust#71896 [71660]: rust-lang/rust#71660 [71322]: rust-lang/rust#71322 [70740]: rust-lang/rust#70740 [cargo/8270]: rust-lang/cargo#8270 [cargo/8325]: rust-lang/cargo#8325 [cargo/8387]: rust-lang/cargo#8387 [`Option::zip`]: https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.zip [`vec::Drain::as_slice`]: https://doc.rust-lang.org/stable/std/vec/struct.Drain.html#method.as_slice

impl From<char> for String

1d0378c

This allows us to write fn char_to_string() -> String { 'a'.into() } which was not possible before.

rust-highfive assigned sfackler Jun 18, 2020

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jun 18, 2020

jonas-schievink added relnotes Marks issues that should be documented in the release notes of the next release. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. labels Jun 18, 2020

jonas-schievink added this to the 1.45 milestone Jun 18, 2020

add test for char into string

2cde493

rust-highfive assigned dtolnay and unassigned sfackler Jun 18, 2020

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 Jun 18, 2020

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 Jun 19, 2020

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 Jun 30, 2020

dtolnay approved these changes Jun 30, 2020

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Manishearth mentioned this pull request Jul 1, 2020

Rollup of 13 pull requests #73907

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Rollup of 15 pull requests #73913

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Rollup of 10 pull requests #73923

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Rollup of 17 pull requests #73924

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Set MSRV as 1.46 prisma/connection-string#14

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impl From<char> for String #73466

impl From<char> for String #73466

matthiaskrgr commented Jun 18, 2020 •

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tesuji commented Jun 18, 2020

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edited by withoutboats

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dtolnay commented Jun 30, 2020

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pickfire commented Jul 1, 2020

dtolnay commented Jul 1, 2020

impl From<char> for String #73466

impl From<char> for String #73466

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