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What this Rust ownership and borrowing question tests

This is a medium-difficulty Rust question that probes your understanding of the language's core ownership system and borrowing rules. Rather than testing raw syntax knowledge, it challenges you to trace how Rust's compiler enforces memory safety—specifically, how moves, references, and scope interact in practice.

To solve it, you need to mentally execute the code and reason about what the compiler would permit or reject. This means understanding when a value moves versus when it's borrowed, what happens to bindings after a move, and how lifetimes constrain reference validity. Quant firms and systems teams often use these questions to confirm that a Rust candidate has internalized ownership semantics rather than just memorized patterns.

• Move semantics and ownership transfer
• Mutable vs. immutable borrows
• Compiler rejection and error messages
• Scope and lifetime constraints