Borrow Trouble

What this Rust borrowing question tests

This is an easy question designed to check your understanding of Rust's ownership and borrowing rules—the core constraint that separates Rust from most other languages. It asks you to predict what the compiler will do when you try to build and execute a specific code snippet.

Solving it requires you to reason about how Rust tracks mutable and immutable references, when borrows are in scope, and what violations trigger compile-time errors. Even experienced developers sometimes trip over the precise interaction between lifetime scoping and reference validity, making this a practical check of your mental model.

• Immutable vs. mutable references
• Borrow scope and the non-lexical lifetimes (NLL) rules
• Compiler error messages and their root causes
• How Rust prevents data races at compile time