Tracking Issue for `fmt_from_fn`

[jmillikin]

Feature gate: #![feature(fmt_from_fn)]

This is a tracking issue for core::fmt::from_fn, split off from [117729] Tracking issue for debug_closure_helpers.

ACP: rust-lang/libs-team#288

Public API

// core::fmt

pub fn from_fn<F>(f: F) -> FromFn<F>
where
    F: Fn(&mut Formatter<'_>) -> Result
{
    FromFn(f)
}

pub struct FromFn<F>(F);

impl<F> fmt::Debug for FromFn<F>
where
    F: Fn(&mut fmt::Formatter<'_>) -> fmt::Result;

impl<F> fmt::Display for FromFn<F>
where
    F: Fn(&mut fmt::Formatter<'_>) -> fmt::Result;

Steps / History

(Remember to update the S-tracking-* label when checking boxes.)

• Implementation: Closure-consuming helper functions for fmt::Debug helpers #117730
• Update to from_fn API: Replace std::fmt:FormatterFn with std::fmt::from_fn #129017
• Final comment period (FCP)¹
• Stabilization PR

Unresolved Questions

• None yet.

Footnotes

1. https://std-dev-guide.rust-lang.org/feature-lifecycle/stabilization.html ↩

[jmillikin]

Proposed stabilization PR: #145915

[Amanieu]

@rfcbot merge

[rust-rfcbot]

Team member @Amanieu has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Amanieu
• @BurntSushi
• @dtolnay
• @joshtriplett
• @m-ou-se
• @the8472

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.

[Amanieu]

I believe the motivation for adding the bounds on F directly on the struct no longer applies since this is now constructed using from_fn instead of having a pub field.