Stabilize `const_constructor` by matthewjasper · Pull Request #65188 · rust-lang/rust

matthewjasper · 2019-10-07T20:13:54Z

Stabilization proposal

I propose that we stabilize #![feature(const_constructor)].

Tracking issue: #61456
Version target: 1.40 (2019-11-05 => beta, 2019-12-19 => stable).

What is stabilized

User guide

Tuple struct and tuple variant constructors are now considered to be constant functions. As such a call expression where the callee has a tuple struct or variant constructor "function item" type can be called:

constfnmake_options(){// These already work because they are special cased:Some(0);(Option::Some)(1);// These also work now:let f = Option::Some;f(2);{Option::Some}(3);
<Option<_>>::Some(5);}

Motivation

Consistency with other const fn. Consistency between syntactic path forms.

This should also ensure that constructors implement const Fn traits and can be coerced to const fn function pointers, if they are introduced.

Tests

ui/consts/const_constructor/const-construct-call.rs - Tests various syntactic forms, use in both const fn and const items, and constructors in both the current and extern crates.
ui/consts/const_constructor/const_constructor_qpath.rs - Tests that type qualified paths to enum variants are also considered to be const fn.(Self::EnumVariant not considered const fn #64247)

r? @oli-obk

Closes#61456
Closes#64247

Centril · 2019-10-08T02:56:25Z

Thanks for the report!
I also propose that we do indeed stabilize const_constructor.

@rfcbot merge

r? @Centril r=me once FCP completes.

rfcbot · 2019-10-08T03:47:54Z

Team member @Centril 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.

pnkfelix · 2019-10-17T19:00:27Z

as described, this seems fine to me.

I would like to note that another case where const constructors arise is in the context of patterns, e.g.:

#[derive(PartialEq,Eq)]structHi(i32);constfnhi() -> Hi{Hi(10)}constC:Hi = hi();fnmain(){matchHi(10){self::C => println!("matched"),
_ => println!("other"),}}

But as far as I can tell, the change being suggested here does not introduce any interesting changes to our behavior for such cases.

pnkfelix · 2019-10-17T19:00:46Z

@rfcbot reviewed

rfcbot · 2019-10-17T19:00:50Z

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

bors · 2019-10-25T14:35:11Z

☔ The latest upstream changes (presumably #65804) made this pull request unmergeable. Please resolve the merge conflicts.

rfcbot · 2019-10-27T19:00:58Z

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.

matthewjasper · 2019-10-27T21:26:28Z

@bors r=Centril

bors · 2019-10-27T21:26:29Z

📌 Commit 170718c has been approved by Centril

bors · 2019-10-27T23:55:33Z

⌛ Testing commit 170718c with merge 077619e...

@oli-obk

…entril Stabilize `const_constructor` # Stabilization proposal I propose that we stabilize `#![feature(const_constructor)]`. Tracking issue: #61456 Version target: 1.40 (2019-11-05 => beta, 2019-12-19 => stable). ## What is stabilized ### User guide Tuple struct and tuple variant constructors are now considered to be constant functions. As such a call expression where the callee has a tuple struct or variant constructor "function item" type can be called: ```rust const fn make_options() { // These already work because they are special cased: Some(0); (Option::Some)(1); // These also work now: let f = Option::Some; f(2); {Option::Some}(3); <Option<_>>::Some(5); } ``` ### Motivation Consistency with other `const fn`. Consistency between syntactic path forms. This should also ensure that constructors implement `const Fn` traits and can be coerced to `const fn` function pointers, if they are introduced. ## Tests * [ui/consts/const_constructor/const-construct-call.rs](https://github.com/rust-lang/rust/blob/0d75ab2293a106eb674ac01860910cfc1580837e/src/test/ui/consts/const_constructor/const-construct-call.rs) - Tests various syntactic forms, use in both `const fn` and `const` items, and constructors in both the current and extern crates. * [ui/consts/const_constructor/const_constructor_qpath.rs](https://github.com/rust-lang/rust/blob/1850dfcdabf8258a1f023f26c2c59e96b869dd95/src/test/ui/consts/const_constructor/const_constructor_qpath.rs) - Tests that type qualified paths to enum variants are also considered to be `const fn`.(#64247) r? @oli-obkCloses#61456Closes#64247

bors · 2019-10-28T04:10:33Z

💥 Test timed out

Centril · 2019-10-28T04:22:00Z

@bors retry

bors · 2019-10-28T07:38:55Z

⌛ Testing commit 170718c with merge 03a50ae...

@oli-obk

…entril Stabilize `const_constructor` # Stabilization proposal I propose that we stabilize `#![feature(const_constructor)]`. Tracking issue: #61456 Version target: 1.40 (2019-11-05 => beta, 2019-12-19 => stable). ## What is stabilized ### User guide Tuple struct and tuple variant constructors are now considered to be constant functions. As such a call expression where the callee has a tuple struct or variant constructor "function item" type can be called: ```rust const fn make_options() { // These already work because they are special cased: Some(0); (Option::Some)(1); // These also work now: let f = Option::Some; f(2); {Option::Some}(3); <Option<_>>::Some(5); } ``` ### Motivation Consistency with other `const fn`. Consistency between syntactic path forms. This should also ensure that constructors implement `const Fn` traits and can be coerced to `const fn` function pointers, if they are introduced. ## Tests * [ui/consts/const_constructor/const-construct-call.rs](https://github.com/rust-lang/rust/blob/0d75ab2293a106eb674ac01860910cfc1580837e/src/test/ui/consts/const_constructor/const-construct-call.rs) - Tests various syntactic forms, use in both `const fn` and `const` items, and constructors in both the current and extern crates. * [ui/consts/const_constructor/const_constructor_qpath.rs](https://github.com/rust-lang/rust/blob/1850dfcdabf8258a1f023f26c2c59e96b869dd95/src/test/ui/consts/const_constructor/const_constructor_qpath.rs) - Tests that type qualified paths to enum variants are also considered to be `const fn`.(#64247) r? @oli-obkCloses#61456Closes#64247

bors · 2019-10-28T10:57:20Z

☀️ Test successful - checks-azure
Approved by: Centril
Pushing 03a50ae to master...

jadbox · 2019-11-07T18:16:13Z

Does this improve performance at all when calling these constructors or no?

matthewjasper · 2019-11-08T12:56:49Z

No, this is just fixing inconsistent behaviour.

Version 1.40.0 (2019-12-19) =========================== Language -------- - [You can now use tuple `struct`s and tuple `enum` variant's constructors in `const` contexts.][65188] e.g. ```rust pub struct Point(i32, i32); const ORIGIN: Point = { let constructor = Point; constructor(0, 0) }; ``` - [You can now mark `struct`s, `enum`s, and `enum` variants with the `#[non_exhaustive]` attribute to indicate that there may be variants or fields added in the future.][64639] For example this requires adding a wild-card branch (`_ => {}`) to any match statements on a non-exhaustive `enum`. [(RFC 2008)] - [You can now use function-like procedural macros in `extern` blocks and in type positions.][63931] e.g. `type Generated = macro!();` - [Function-like and attribute procedural macros can now emit `macro_rules!` items, so you can now have your macros generate macros.][64035] - [The `meta` pattern matcher in `macro_rules!` now correctly matches the modern attribute syntax.][63674] For example `(#[$m:meta])` now matches `#[attr]`, `#[attr{tokens}]`, `#[attr[tokens]]`, and `#[attr(tokens)]`. Compiler -------- - [Added tier 3 support\* for the `thumbv7neon-unknown-linux-musleabihf` target.][66103] - [Added tier 3 support for the `aarch64-unknown-none-softfloat` target.][64589] - [Added tier 3 support for the `mips64-unknown-linux-muslabi64`, and `mips64el-unknown-linux-muslabi64` targets.][65843] \* Refer to Rust's [platform support page][forge-platform-support] for more information on Rust's tiered platform support. Libraries --------- - [The `is_power_of_two` method on unsigned numeric types is now a `const` function.][65092] Stabilized APIs --------------- - [`BTreeMap::get_key_value`] - [`HashMap::get_key_value`] - [`Option::as_deref_mut`] - [`Option::as_deref`] - [`Option::flatten`] - [`UdpSocket::peer_addr`] - [`f32::to_be_bytes`] - [`f32::to_le_bytes`] - [`f32::to_ne_bytes`] - [`f64::to_be_bytes`] - [`f64::to_le_bytes`] - [`f64::to_ne_bytes`] - [`f32::from_be_bytes`] - [`f32::from_le_bytes`] - [`f32::from_ne_bytes`] - [`f64::from_be_bytes`] - [`f64::from_le_bytes`] - [`f64::from_ne_bytes`] - [`mem::take`] - [`slice::repeat`] - [`todo!`] Cargo ----- - [Cargo will now always display warnings, rather than only on fresh builds.][cargo/7450] - [Feature flags (except `--all-features`) passed to a virtual workspace will now produce an error.][cargo/7507] Previously these flags were ignored. - [You can now publish `dev-dependencies` without including a `version`.][cargo/7333] Misc ---- - [You can now specify the `#[cfg(doctest)]` attribute to include an item only when running documentation tests with `rustdoc`.][63803] Compatibility Notes ------------------- - [As previously announced, any previous NLL warnings in the 2015 edition are now hard errors.][64221] - [The `include!` macro will now warn if it failed to include the entire file.][64284] The `include!` macro unintentionally only includes the first _expression_ in a file, and this can be unintuitive. This will become either a hard error in a future release, or the behavior may be fixed to include all expressions as expected. - [Using `#[inline]` on function prototypes and consts now emits a warning under `unused_attribute` lint.][65294] Using `#[inline]` anywhere else inside traits or `extern` blocks now correctly emits a hard error. [65294]: rust-lang/rust#65294 [66103]: rust-lang/rust#66103 [65843]: rust-lang/rust#65843 [65188]: rust-lang/rust#65188 [65092]: rust-lang/rust#65092 [64589]: rust-lang/rust#64589 [64639]: rust-lang/rust#64639 [64221]: rust-lang/rust#64221 [64284]: rust-lang/rust#64284 [63931]: rust-lang/rust#63931 [64035]: rust-lang/rust#64035 [63674]: rust-lang/rust#63674 [63803]: rust-lang/rust#63803 [cargo/7450]: rust-lang/cargo#7450 [cargo/7507]: rust-lang/cargo#7507 [cargo/7525]: rust-lang/cargo#7525 [cargo/7333]: rust-lang/cargo#7333 [(rfc 2008)]: https://rust-lang.github.io/rfcs/2008-non-exhaustive.html [`f32::to_be_bytes`]: https://doc.rust-lang.org/std/primitive.f32.html#method.to_be_bytes [`f32::to_le_bytes`]: https://doc.rust-lang.org/std/primitive.f32.html#method.to_le_bytes [`f32::to_ne_bytes`]: https://doc.rust-lang.org/std/primitive.f32.html#method.to_ne_bytes [`f64::to_be_bytes`]: https://doc.rust-lang.org/std/primitive.f64.html#method.to_be_bytes [`f64::to_le_bytes`]: https://doc.rust-lang.org/std/primitive.f64.html#method.to_le_bytes [`f64::to_ne_bytes`]: https://doc.rust-lang.org/std/primitive.f64.html#method.to_ne_bytes [`f32::from_be_bytes`]: https://doc.rust-lang.org/std/primitive.f32.html#method.from_be_bytes [`f32::from_le_bytes`]: https://doc.rust-lang.org/std/primitive.f32.html#method.from_le_bytes [`f32::from_ne_bytes`]: https://doc.rust-lang.org/std/primitive.f32.html#method.from_ne_bytes [`f64::from_be_bytes`]: https://doc.rust-lang.org/std/primitive.f64.html#method.from_be_bytes [`f64::from_le_bytes`]: https://doc.rust-lang.org/std/primitive.f64.html#method.from_le_bytes [`f64::from_ne_bytes`]: https://doc.rust-lang.org/std/primitive.f64.html#method.from_ne_bytes [`option::flatten`]: https://doc.rust-lang.org/std/option/enum.Option.html#method.flatten [`option::as_deref`]: https://doc.rust-lang.org/std/option/enum.Option.html#method.as_deref [`option::as_deref_mut`]: https://doc.rust-lang.org/std/option/enum.Option.html#method.as_deref_mut [`hashmap::get_key_value`]: https://doc.rust-lang.org/std/collections/struct.HashMap.html#method.get_key_value [`btreemap::get_key_value`]: https://doc.rust-lang.org/std/collections/struct.BTreeMap.html#method.get_key_value [`slice::repeat`]: https://doc.rust-lang.org/std/primitive.slice.html#method.repeat [`mem::take`]: https://doc.rust-lang.org/std/mem/fn.take.html [`udpsocket::peer_addr`]: https://doc.rust-lang.org/std/net/struct.UdpSocket.html#method.peer_addr [`todo!`]: https://doc.rust-lang.org/std/macro.todo.html

matthewjasper added the T-lang Relevant to the language team label Oct 7, 2019

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Stabilize const_constructor
170718c

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This was referenced Oct 28, 2019
[rustdoc] stabilize cfg(doctest) #63803
Merged
Organize intrinsics const evaluability checks #61835
Closed
Stabilize the re_rebalance_coherence feature #65879
Merged

matthewjasper deleted the stabilize-const-constructor branch October 28, 2019 19:37

Mark-Simulacrum mentioned this pull request Nov 2, 2019
Compile hangs endlessly in LLVM in await-heavy code when ThinLTO is enabled #66036
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Stabilization proposal

What is stabilized

User guide

Motivation

Tests

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