EmbeddingGemma 2: an open, lightweight multimodal embedding model
deepmind.google·6d ago
AI Engineering
Lobsters·Sep 5·5 min read
Visualizing Rust's Vtables: How dyn Trait Works In Memory
TL;DR
Exploring Rust's dynamic traits reveals how polymorphism is managed in memory, contrasting with C++'s approach. Understanding these mechanisms enhances comprehension of Rust's unique features.
✦ Why It Matters
Dive into Rust's memory management to enhance your understanding of its unique polymorphism features.
Key Takeaways
- Explore Rust's dyn Trait for dynamic polymorphism.
- Understand zero-sized types and their memory implications.
- Utilize Box<dyn Trait> for heterogeneous collections.
- Learn object safety rules for Rust traits.
How It Works
Rust's dyn Trait enables dynamic dispatch by using a wide pointer that contains both a data pointer and a vtable pointer. This allows the program to determine the correct method to call at runtime without embedding the vtable in each object, thus saving memory.
The vtable is shared among instances of the same type, which contrasts with C++ where the vtable is part of the object itself.
⚠ The Catch
Not all Rust traits can be used as dyn Trait due to object safety rules, which restrict methods from returning Self or having generic parameters. This limitation can complicate certain designs that are straightforward in C++.