Iterator Shenanigans

What this Rust iterator behaviour question tests

This is a medium-difficulty Rust language question that probes your understanding of how iterators work—specifically, the interaction between iterator consumption, borrowing rules, and method chaining. It rewards precision about Rust's ownership model and iterator semantics.

To work through questions like this, you need to trace how Rust's iterator adapters (like map, filter, and collect) consume or borrow their inputs, and how the borrow checker enforces those rules in practice. The question tests whether you can predict runtime behaviour by reasoning about what the compiler permits and how iterator lazy evaluation works.

• Iterator consumption and when values are moved vs. borrowed
• Chaining iterator adapters and order of evaluation
• The relationship between iterator type signatures and borrowing constraints