Tracking Issue for `#![feature(offset_of)]`

[WaffleLapkin]

Feature gates tracked by this issue:

• #![feature(offset_of)]
• #![feature(offset_of_enum)] -> moved to Tracking Issue for enum access in offset_of #120141

This is a tracking issue for the offset_of! macro which evaluates to a constant
containing the offset in bytes of a field inside some type (rust-lang/rfcs#3308).

Public API

// core::mem

pub macro offset_of($Container:ty, $field:tt $(,)?) {
    // ...implementation defined...
}

Steps / History

• Implementation: Add offset_of! macro (RFC 3308) #106934
• Split off offset_of_enum: Feature gate enums in offset_of #117537
• Final comment period (FCP)¹: old, new
• Stabilization PR: Stabilize single-field offset_of #118799

Possible future extensions / work

• Support for static alignment DSTs (struct Example(u32, [u8]))
• Support for enums: Support enum variants in offset_of! #114208
• Improving diagnostics around the macro errors

Unresolved Questions

• None yet.

Footnotes

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

[tgross35]

It looks like #106934 is the implementation PR, you may be able to link it in the readme

[est31]

Some things that could get tests:

• offset_of!(Self, ...) works, if and only if it's inside an impl block.
• the return type of offset_of!() is usize: some code that tries to use it as usize -> works. some code that tries to use it as u8/isize -> fails.

Edit: #111665