We’re launching Lyria 3.5 in Google Flow Music, with advances across musicality, lyrics, vocals, and creative control
deepmind.google·6d ago
AI Engineering
Lobsters·Jun 18·5 min read
offset_of! slices
TL;DR
Rust's std::mem::offset_of! macro computes the byte offset of struct fields at compile time, but it has limitations with unsized fields.
✦ Why It Matters
Engineers can now safely compute offsets for slice fields in stable Rust, improving memory management capabilities.
Key Takeaways
- Use std::mem::offset_of! for sized fields.
- Construct fake instances for slice fields.
- Avoid offsets larger than 64k.
- Ensure valid memory for pointer calculations.
Full Summary
In Rust, the std::mem::offset_of! macro is useful for determining the byte offset of fields within structs at compile time, but it cannot be used with unsized fields like slices.
To address this limitation, a method was created that constructs a fake instance of the struct containing the slice field, allowing the offset to be calculated safely. This method leverages pointer casting and ensures that the fake instance points to valid memory by using a large byte array.
While offsets larger than 64k are not supported, this approach effectively circumvents the restrictions of unsized types. The implementation is particularly relevant for developers working with dynamically sized types in Rust, as it enables compile-time calculations without risking undefined behavior.
Overall, this technique enhances the usability of Rust's memory management features for advanced applications.