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Tracking Issue for const_ptr_as_ref #91822

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lilasta opened this issue Dec 12, 2021 · 8 comments · Fixed by #131177
Closed
1 of 3 tasks

Tracking Issue for const_ptr_as_ref #91822

lilasta opened this issue Dec 12, 2021 · 8 comments · Fixed by #131177
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C-tracking-issue Category: A tracking issue for an RFC or an unstable feature. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. finished-final-comment-period The final comment period is finished for this PR / Issue. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue.

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@lilasta
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lilasta commented Dec 12, 2021

Feature gate: #![feature(const_ptr_as_ref)]

Public API

impl<T: ?Sized> NonNull<T> {
    pub const unsafe fn as_mut<'a>(&mut self) -> &'a mut T;
}

Steps / History

Unresolved Questions

  • None yet.
@lilasta lilasta added C-tracking-issue Category: A tracking issue for an RFC or an unstable feature. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. labels Dec 12, 2021
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Dec 21, 2021
Make `PTR::as_ref` and similar methods `const`.

Tracking issue: rust-lang#91822
Feature gate: `#![feature(const_ptr_as_ref)]`

```rust
// core::ptr
impl<T: ?Sized> *const T {
    pub const unsafe fn as_ref<'a>(self) -> Option<&'a T>;
    pub const unsafe fn as_uninit_ref<'a>(self) -> Option<&'a MaybeUninit<T>>
    where
        T: Sized;
    pub const unsafe fn as_uninit_slice<'a>(self) -> Option<&'a [MaybeUninit<T>]>;
}

impl<T: ?Sized> *mut T {
    pub const unsafe fn as_ref<'a>(self) -> Option<&'a T>;
    pub const unsafe fn as_uninit_ref<'a>(self) -> Option<&'a MaybeUninit<T>>
    where
        T: Sized;
    pub const unsafe fn as_mut<'a>(self) -> Option<&'a mut T>;
    pub const unsafe fn as_uninit_mut<'a>(self) -> Option<&'a mut MaybeUninit<T>>
    where
        T: Sized;
    pub const unsafe fn as_uninit_slice<'a>(self) -> Option<&'a [MaybeUninit<T>]>;
    pub const unsafe fn as_uninit_slice_mut<'a>(self) -> Option<&'a mut [MaybeUninit<T>]>;
}

impl<T: Sized> NonNull<T> {
    pub const unsafe fn as_uninit_ref<'a>(&self) -> &'a MaybeUninit<T>;
    pub const unsafe fn as_uninit_mut<'a>(&mut self) -> &'a mut MaybeUninit<T>;
}

impl<T: ?Sized> NonNull<T> {
    pub const unsafe fn as_ref<'a>(&self) -> &'a T;
    pub const unsafe fn as_mut<'a>(&mut self) -> &'a mut T;
    pub const unsafe fn as_uninit_slice<'a>(&self) -> &'a [MaybeUninit<T>];
    pub const unsafe fn as_uninit_slice_mut<'a>(&self) -> &'a mut [MaybeUninit<T>];
}
```
Dylan-DPC added a commit to Dylan-DPC/rust that referenced this issue Jul 30, 2023
`const`-stablilize `NonNull::as_ref`

A bunch of pointer to reference methods have been made unstably const some time ago in rust-lang#91823 under the feature gate `const_ptr_as_ref`.
Out of these, `NonNull::as_ref` can be implemented as a `const fn` in stable rust today, so i hereby propose to const stabilize this function only.

Tracking issue: rust-lang#91822

`@rustbot` label +T-libs-api -T-libs
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Jul 30, 2023
`const`-stablilize `NonNull::as_ref`

A bunch of pointer to reference methods have been made unstably const some time ago in rust-lang#91823 under the feature gate `const_ptr_as_ref`.
Out of these, `NonNull::as_ref` can be implemented as a `const fn` in stable rust today, so i hereby propose to const stabilize this function only.

Tracking issue: rust-lang#91822

``@rustbot`` label +T-libs-api -T-libs
workingjubilee added a commit to workingjubilee/rustc that referenced this issue May 3, 2024
… r=workingjubilee

Implement ptr_as_ref_unchecked

Implementation of rust-lang#122034.

Prefixed the feature name with `ptr_` for clarity.

Linked const-unstability to rust-lang#91822, so the post there should probably be updated to mentions the 3 new methods when/if this PR is merged.
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue May 3, 2024
… r=workingjubilee

Implement ptr_as_ref_unchecked

Implementation of rust-lang#122034.

Prefixed the feature name with `ptr_` for clarity.

Linked const-unstability to rust-lang#91822, so the post there should probably be updated to mentions the 3 new methods when/if this PR is merged.
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue May 3, 2024
… r=workingjubilee

Implement ptr_as_ref_unchecked

Implementation of rust-lang#122034.

Prefixed the feature name with `ptr_` for clarity.

Linked const-unstability to rust-lang#91822, so the post there should probably be updated to mentions the 3 new methods when/if this PR is merged.
rust-timer added a commit to rust-lang-ci/rust that referenced this issue May 3, 2024
Rollup merge of rust-lang#122492 - GrigorenkoPV:ptr_as_ref_unchecked, r=workingjubilee

Implement ptr_as_ref_unchecked

Implementation of rust-lang#122034.

Prefixed the feature name with `ptr_` for clarity.

Linked const-unstability to rust-lang#91822, so the post there should probably be updated to mentions the 3 new methods when/if this PR is merged.
@GrigorenkoPV
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Hello!

Now that #122492 has been merged, 3 new methods are also const-gated behind this flag

  • <*const T>::as_ref_unchecked
  • <*mut T>::as_ref_unchecked
  • <*mut T>::as_mut_unchecked

Should they be added to the OP?

@lilasta
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lilasta commented May 4, 2024

I have added them to the list.

@RalfJung
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RalfJung commented Sep 8, 2024

@rust-lang/libs-api I propose we const-stabilize the subset of the methods above that are stable for non-const calls:

// core::ptr
impl<T: ?Sized> *const T {
    pub const unsafe fn as_ref<'a>(self) -> Option<&'a T>;
}

impl<T: ?Sized> *mut T {
    pub const unsafe fn as_ref<'a>(self) -> Option<&'a T>;
    pub const unsafe fn as_mut<'a>(self) -> Option<&'a mut T>;
}

impl<T: ?Sized> NonNull<T> {
    pub const unsafe fn as_mut<'a>(&mut self) -> &'a mut T;
}

The rest should be moved to the feature gate tracking their general stability, no separate const-feature-gate is needed. (EDIT: that is happening in #130164)

@RalfJung RalfJung added the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Sep 8, 2024
@RalfJung
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RalfJung commented Sep 8, 2024

Ah wait, the Option-returning ones are non-trivial since they require the is_null test... they should be moved under the const_ptr_is_null feature gate (#74939).

So then only one function is left to be stabilized here: NonNull::as_mut.

@dtolnay
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dtolnay commented Sep 9, 2024

@rfcbot fcp merge

Subsequent to #129195, we are ready to stabilize const on NonNull::as_mut:

pub const unsafe fn as_mut<'a>(&mut self) -> &'a mut T {
// SAFETY: the caller must guarantee that `self` meets all the
// requirements for a mutable reference.
unsafe { &mut *self.as_ptr() }
}

This function is the mut analog of NonNull::as_ref for which we stabilized const in #102198.

pub const unsafe fn as_ref<'a>(&self) -> &'a T {
// SAFETY: the caller must guarantee that `self` meets all the
// requirements for a reference.
// `cast_const` avoids a mutable raw pointer deref.
unsafe { &*self.as_ptr().cast_const() }
}

@rfcbot
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rfcbot commented Sep 9, 2024

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.

@rfcbot 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 Sep 9, 2024
@dtolnay dtolnay removed the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Sep 9, 2024
workingjubilee added a commit to workingjubilee/rustc that referenced this issue Sep 10, 2024
move some const fn out of the const_ptr_as_ref feature

When a `const fn` is still `#[unstable]`, it should generally use the same feature to track its regular stability and const-stability. Then when that feature moves towards stabilization we can decide whether the const-ness can be stabilized as well, or whether it should be moved into a new feature.

Also, functions like `ptr::as_ref` (which returns an `Option<&mut T>`) require `is_null`, which is tricky and blocked on some design concerns (see rust-lang#74939). So move those to the is_null feature gate, as they should be stabilized together with `ptr.is_null()`.

Affects rust-lang#91822, rust-lang#122034, rust-lang#75402, rust-lang#74939
workingjubilee added a commit to workingjubilee/rustc that referenced this issue Sep 10, 2024
move some const fn out of the const_ptr_as_ref feature

When a `const fn` is still `#[unstable]`, it should generally use the same feature to track its regular stability and const-stability. Then when that feature moves towards stabilization we can decide whether the const-ness can be stabilized as well, or whether it should be moved into a new feature.

Also, functions like `ptr::as_ref` (which returns an `Option<&mut T>`) require `is_null`, which is tricky and blocked on some design concerns (see rust-lang#74939). So move those to the is_null feature gate, as they should be stabilized together with `ptr.is_null()`.

Affects rust-lang#91822, rust-lang#122034, rust-lang#75402, rust-lang#74939
rust-timer added a commit to rust-lang-ci/rust that referenced this issue Sep 10, 2024
Rollup merge of rust-lang#130164 - RalfJung:const_ptr_as_ref, r=dtolnay

move some const fn out of the const_ptr_as_ref feature

When a `const fn` is still `#[unstable]`, it should generally use the same feature to track its regular stability and const-stability. Then when that feature moves towards stabilization we can decide whether the const-ness can be stabilized as well, or whether it should be moved into a new feature.

Also, functions like `ptr::as_ref` (which returns an `Option<&mut T>`) require `is_null`, which is tricky and blocked on some design concerns (see rust-lang#74939). So move those to the is_null feature gate, as they should be stabilized together with `ptr.is_null()`.

Affects rust-lang#91822, rust-lang#122034, rust-lang#75402, rust-lang#74939
@rfcbot 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 Sep 24, 2024
@rfcbot
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rfcbot commented Sep 24, 2024

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

@rfcbot rfcbot added finished-final-comment-period The final comment period is finished for this PR / Issue. to-announce Announce this issue on triage meeting and removed final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. labels Oct 4, 2024
@rfcbot
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rfcbot commented Oct 4, 2024

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.

This will be merged soon.

workingjubilee added a commit to workingjubilee/rustc that referenced this issue Oct 4, 2024
…-referees, r=tgross35

 Stabilize 5 `const_mut_refs`-dependent API

Since `const_mut_refs` and `const_refs_to_cell` have been stabilized, we now may create mutable references inside our library API. Thus we now stabilize the `const fn` version of these public library APIs which required such in their implementation:
- const `NonNull::as_mut` rust-lang#91822 (comment)
- const `slice::{first,last}_mut`: rust-lang#83570 (comment)
- const `str::as_{mut_ptr,bytes_mut}`: rust-lang#130086 (comment)
- const `str::from_utf8_unchecked_mut`: rust-lang#91005 (comment)
- const `UnsafeCell::get_mut`: rust-lang#88836 (comment)
workingjubilee added a commit to workingjubilee/rustc that referenced this issue Oct 4, 2024
…-referees, r=tgross35

 Stabilize 5 `const_mut_refs`-dependent API

Since `const_mut_refs` and `const_refs_to_cell` have been stabilized, we now may create mutable references inside our library API. Thus we now stabilize the `const fn` version of these public library APIs which required such in their implementation:
- const `NonNull::as_mut` rust-lang#91822 (comment)
- const `slice::{first,last}_mut`: rust-lang#83570 (comment)
- const `str::as_{mut_ptr,bytes_mut}`: rust-lang#130086 (comment)
- const `str::from_utf8_unchecked_mut`: rust-lang#91005 (comment)
- const `UnsafeCell::get_mut`: rust-lang#88836 (comment)
workingjubilee added a commit to workingjubilee/rustc that referenced this issue Oct 4, 2024
…-referees, r=tgross35

 Stabilize 5 `const_mut_refs`-dependent API

Since `const_mut_refs` and `const_refs_to_cell` have been stabilized, we now may create mutable references inside our library API. Thus we now stabilize the `const fn` version of these public library APIs which required such in their implementation:
- const `NonNull::as_mut` rust-lang#91822 (comment)
- const `slice::{first,last}_mut`: rust-lang#83570 (comment)
- const `str::as_{mut_ptr,bytes_mut}`: rust-lang#130086 (comment)
- const `str::from_utf8_unchecked_mut`: rust-lang#91005 (comment)
- const `UnsafeCell::get_mut`: rust-lang#88836 (comment)
rust-timer added a commit to rust-lang-ci/rust that referenced this issue Oct 5, 2024
Rollup merge of rust-lang#131177 - workingjubilee:stabilize-const-mut-referees, r=tgross35

 Stabilize 5 `const_mut_refs`-dependent API

Since `const_mut_refs` and `const_refs_to_cell` have been stabilized, we now may create mutable references inside our library API. Thus we now stabilize the `const fn` version of these public library APIs which required such in their implementation:
- const `NonNull::as_mut` rust-lang#91822 (comment)
- const `slice::{first,last}_mut`: rust-lang#83570 (comment)
- const `str::as_{mut_ptr,bytes_mut}`: rust-lang#130086 (comment)
- const `str::from_utf8_unchecked_mut`: rust-lang#91005 (comment)
- const `UnsafeCell::get_mut`: rust-lang#88836 (comment)
@apiraino apiraino removed the to-announce Announce this issue on triage meeting label Oct 17, 2024
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C-tracking-issue Category: A tracking issue for an RFC or an unstable feature. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. finished-final-comment-period The final comment period is finished for this PR / Issue. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue.
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6 participants