Tracking Issue for `inherent_str_constructors`

[robertbastian]

Feature gate: #![feature(inherent_str_constructors)]

This is a tracking issue for inherent str constructors.

Public API

• str::from_utf8
• str::from_utf8_mut
• str::from_utf8_unchecked
• str::from_utf8_unchecked_mut

Steps / History

• ACP: Make core::str::from_utf8* methods available on the str type libs-team#398
• Implementation: implement inherent str constructors #136517
• Final comment period (FCP)¹
• Stabilization PR

Unresolved Questions

• None yet.

Footnotes

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

[hanna-kruppe]

I would like to request stabilization of these constructors. Yes, they only landed in nightly a few days ago, but there shouldn't be any need to gather more experience with them since they're identical in every way to existing APIs that have been stable forever, except not requiring an import of the str module. On the contrary, them existing unstably currently degrades compiler diagnostics, so stabilizing them ASAP would be helpful.

Implementation history

• API change proposal: Make core::str::from_utf8* methods available on the str type libs-team#398
• Implementation: implement inherent str constructors #136517
• The first PR trying to implement it got bogged down in trying to migrate existing in-tree uses to the new API and raised the question of deprecating the non-inherent functions in a future version. As @tgross35 said there, none of that seems necessary or advisable before the inherent constructors are stabilized.

API summary

impl str {
    pub const fn from_utf8(v: &[u8]) -> Result<&str, Utf8Error>;
    pub fn from_utf8_mut(v: &mut [u8]) -> Result<&mut str, Utf8Error>;
    pub const unsafe fn from_utf8_unchecked(v: &[u8]) -> &str;
    pub const unsafe fn from_utf8_unchecked_mut(v: &mut [u8]) -> &mut str;
}

The stable *_mut constructors The stable core::str::from_utf8_mut is not stably const yet, so the inherent equivalent should not be const-stabilized either at this point (but see #136668). The other three constructors are stably const, including from_utf8_unchecked_mut since 1.83.

Experience report

As @joshtriplett wrote on the ACP:

The reaction in today's @rust-lang/libs-api meeting was "why didn't we do this years ago".

I just tried it on a personal project, removing four imports of {std,core}::str and adding #![feature(inherent_str_constructors)] to the respective crate roots instead. Worked as expected. But I'm not going to commit those changes because having to add the feature flag wouldn't be worth it even if that project already required nightly.

[joshtriplett]

@rfcbot merge

[rfcbot]

Team member @joshtriplett 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

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]

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