How big is this str?

Understanding string size and memory layout in Rust

This easy question tests whether you understand how Rust represents strings in memory and can reason about the difference between string types and their on-stack vs. heap storage. It's a foundational piece of knowledge for any Rust developer working on systems where memory efficiency or low-latency behaviour matters.

The question asks you to determine the byte size of a string value on a 64-bit system. To answer it correctly, you need to know the internal structure of Rust's string type—specifically how many fields it holds, how large each field is, and how they are laid out in memory. This touches on Rust's ownership model and the distinction between stack-allocated metadata and heap-allocated data.

• Stack vs. heap allocation in Rust
• Size of pointers and length metadata
• String type internals and capacity tracking