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Tracking Issue for comparing TypeId in const items #101871

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raldone01 opened this issue Sep 15, 2022 · 0 comments
Open
1 of 4 tasks

Tracking Issue for comparing TypeId in const items #101871

raldone01 opened this issue Sep 15, 2022 · 0 comments
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C-tracking-issue Category: A tracking issue for an RFC or an unstable feature. T-lang Relevant to the language team, which will review and decide on the PR/issue. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue.

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@raldone01
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raldone01 commented Sep 15, 2022 •
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Feature gate: #![feature(const_cmp_type_id)]

This is a tracking issue for comparing TypeId in const items.

Public API

impl const PartialEq for TypeId {}
impl const PartialOrd for TypeId {}
impl const Ord for TypeId {}

Steps / History

Unresolved Questions

  • Making these const precludes some possible implementations, such as the one where TypeId includes a pointer to a static as proposed in TypeId: use a (v0) mangled type to remain sound in the face of hash collisions. #95845. This const-ness should not be stabilized without an explicit decision that we never want such an implementation.

    raldone01: I don't think adding a 'static pointer would be a problem as the contents of the pointer would be compared and not the pointer addresses.

Footnotes

  1. https://std-dev-guide.rust-lang.org/feature-lifecycle/stabilization.html ↩
@raldone01 raldone01 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 Sep 15, 2022
@raldone01 raldone01 mentioned this issue Sep 15, 2022
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@scottmcm scottmcm added the T-lang Relevant to the language team, which will review and decide on the PR/issue. label Sep 28, 2022
Dylan-DPC added a commit to Dylan-DPC/rust that referenced this issue Jan 17, 2023
@Dylan-DPC
Rollup merge of rust-lang#101698 - raldone01:feat/const_cmp_typeid, r…
09faa26 
…=scottmcm

Constify `TypeId` ordering impls

Tracking issue: rust-lang#101871

Adding const ordering to `TypeId` allows rtti crates to optimize some casting scenarios (without transmuting to `u64`). This would also prevent these crates from breaking if the underlying type is changed from `u64` to something different.

Feature gate: `#![feature(const_cmp_type_id)]`
@KodrAus KodrAus mentioned this issue May 28, 2023
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C-tracking-issue Category: A tracking issue for an RFC or an unstable feature. T-lang Relevant to the language team, which will review and decide on the PR/issue. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue.
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@scottmcm @raldone01