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Tracking Issue for `ptr::fn_addr_eq` #129322

Open Urgau opened 2 months ago

Urgau commented 2 months ago

Feature gate: #![feature(ptr_fn_addr_eq)]

This is a tracking issue for std::ptr::fn_addr_eq

Compares the addresses of the two function pointers for equality.

Public API

// core::ptr

/// Compares the *addresses* of the two function pointers for equality.
///
/// Function pointers comparisons can have surprising results since
/// they are never guaranteed to be unique and could vary between different
/// code generation units. Furthermore, different functions could have the
/// same address after being merged together.
///
/// This is the same as `f == g` but using this function makes clear
/// that you are aware of these potentially surprising semantics.
pub fn fn_addr_eq<T: FnPtr, U: FnPtr>(f: T, g: U) -> bool {
    f.addr() == g.addr()
}

Steps / History

Unresolved Questions

Urgau commented 2 weeks ago

T-lang as started an FCP for adding a lint against function pointer comparisons and would like to use this method ptr::fn_addr_eq as recommendation to suppress the lint and hang documentation about caveats.

Stabilization Report

Implementation History

API Summary

// core::ptr

/// Compares the *addresses* of the two function pointers for equality.
///
/// Function pointers comparisons can have surprising results since
/// they are never guaranteed to be unique and could vary between different
/// code generation units. Furthermore, different functions could have the
/// same address after being merged together.
///
/// This is the same as `f == g` but using this function makes clear
/// that you are aware of these potentially surprising semantics.
pub fn fn_addr_eq<T: FnPtr, U: FnPtr>(f: T, g: U) -> bool {
    f.addr() == g.addr()
}

The std::marker::FnPtr bound

The FnPtr marker trait is not stable and would be not stabilized by this FCP, but this commits us to having such trait (even in this unstable form).

cc @rust-lang/lang (regarding the FnPtr bound) cc @rust-lang/libs-api

dtolnay commented 2 weeks ago

@rfcbot fcp merge

rfcbot commented 2 weeks ago

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!

cc @rust-lang/lang-advisors: FCP proposed for lang, please feel free to register concerns. See this document for info about what commands tagged team members can give me.

traviscross commented 2 weeks ago

@rfcbot reviewed

nikomatsakis commented 1 day ago

@rfcbot reviewed

traviscross commented 1 day ago

@rustbot labels -I-lang-nominated

We discussed this in triage today. We've now unanimously checked off on the lang side. We appreciate @rust-lang/libs-api for moving this forward in support of the pending lang work.