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Answer: The iterator pattern allows you to perform some task on a sequence of items in turn. In Rust, iterators are lazy, meaning they have no effect until you call methods that consume the iterator to use it up. (S1)

How they work

• An iterator is responsible for the logic of iterating over each item and determining when the sequence has finished. (S1)
• Implementing the Iterator trait requires that you also define an Item type, and this Item type is used in the return type of the next method. (S1)
• Calling the next method on an iterator changes internal state that the iterator uses to keep track of where it is in the sequence. (S1)
• Each call to next eats up an item from the iterator. (S1)

In practice

• The Iterator trait is used to implement iterators over collections such as arrays. (S2)
• As a point of convenience for common situations, the for construct turns some collections into iterators using the .into_iter() method. (S2)

Claims

• id: C1 claim: Rust iterators are lazy. source: S1 evidence: "In Rust, iterators are lazy"
• id: C2 claim: Iterator requires an Item type. source: S1 evidence: "this code says implementing the Iterator trait requires that you also define"
• id: C3 claim: next changes internal state. source: S1 evidence: "Calling the next method on an iterator"
• id: C4 claim: for uses into_iter. source: S2 evidence: "turns some collections into iterators using the .into_iter() method."

Sources

• [S1] Processing a Series of Items with Iterators - The Rust Programming Language. The Rust Programming Language. https://doc.rust-lang.org/book/ch13-02-iterators.html . License: MIT or Apache-2.0 (rust-lang/book; Copyright (c) 2010 The Rust Project Developers; https://github.com/rust-lang/book/blob/main/LICENSE-MIT). Accessed 2026-11-04.
• [S2] Iterators - Rust By Example. Rust by Example. https://doc.rust-lang.org/rust-by-example/trait/iter.html . License: MIT or Apache-2.0 (rust-lang/rust-by-example; Copyright (c) 2014 Jorge Aparicio; https://github.com/rust-lang/rust-by-example/blob/master/LICENSE-MIT). Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_yn1r54fv,
  author = {{iinventedlight}},
  title = {{Iterators in Rust}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/rust-iterators/},
  note = {Permanent ID iil:note:yn1r54fv. License: CC-BY-4.0.},
}

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