# Iterators & Closures (Rust)

> Iterator trait, iterator adapters (map, filter, fold), closure syntax, move closures, Fn traits

- 22 interview questions
- Mid-Level
- [Interview Questions: Rust](https://sharpskill.dev/en/technologies/rust/interview-questions.md)

## 1. Which trait must a type implement to be usable in a for loop in Rust?

**Answer**

The IntoIterator trait allows a type to be converted into an iterator. The for loop automatically calls into_iter() on the expression. Types like Vec, arrays and ranges implement this trait by default, which allows iterating over them directly with for.

## 2. Which method of the Iterator trait must be implemented?

**Answer**

The next() method is the only required method of the Iterator trait. It returns Option<Self::Item>, either Some(item) if there are remaining elements, or None when iteration is complete. All other methods like map, filter or collect have default implementations based on next().

## 3. What is the difference between iter(), iter_mut() and into_iter() on a Vec<T>?

**Answer**

iter() returns an iterator over immutable references (&T), iter_mut() over mutable references (&mut T), and into_iter() consumes the Vec and returns elements by value (T). The choice depends on whether you want to read, modify or take ownership of the elements.

## 19 more questions available

- What is a lazy iterator in Rust and why is it important?
- What is the correct syntax to define a closure that takes two i32 parameters and returns their sum?

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## Other Rust interview topics

- [Rust Basics](https://sharpskill.dev/en/technologies/rust/interview-questions/rust-basics.md): 25 questions, Junior
- [Ownership & Borrowing](https://sharpskill.dev/en/technologies/rust/interview-questions/ownership-borrowing.md): 22 questions, Junior
- [Structs & Enums](https://sharpskill.dev/en/technologies/rust/interview-questions/structs-enums.md): 20 questions, Junior
- [Error Handling](https://sharpskill.dev/en/technologies/rust/interview-questions/error-handling.md): 18 questions, Junior
- [Collections](https://sharpskill.dev/en/technologies/rust/interview-questions/collections.md): 20 questions, Junior
- [Modules & Packages](https://sharpskill.dev/en/technologies/rust/interview-questions/modules-packages.md): 18 questions, Junior
- [Traits](https://sharpskill.dev/en/technologies/rust/interview-questions/traits.md): 22 questions, Mid-Level
- [Generics](https://sharpskill.dev/en/technologies/rust/interview-questions/generics.md): 20 questions, Mid-Level
- [Lifetimes](https://sharpskill.dev/en/technologies/rust/interview-questions/lifetimes.md): 20 questions, Mid-Level
- [Smart Pointers](https://sharpskill.dev/en/technologies/rust/interview-questions/smart-pointers.md): 22 questions, Mid-Level
- [Concurrency Basics](https://sharpskill.dev/en/technologies/rust/interview-questions/concurrency-basics.md): 20 questions, Mid-Level
- [async/await](https://sharpskill.dev/en/technologies/rust/interview-questions/async-await.md): 22 questions, Mid-Level
- [Testing](https://sharpskill.dev/en/technologies/rust/interview-questions/testing.md): 18 questions, Mid-Level
- [Cargo & Ecosystem](https://sharpskill.dev/en/technologies/rust/interview-questions/cargo-ecosystem.md): 18 questions, Mid-Level
- [Pattern Matching](https://sharpskill.dev/en/technologies/rust/interview-questions/pattern-matching.md): 18 questions, Mid-Level
- [Macros](https://sharpskill.dev/en/technologies/rust/interview-questions/macros.md): 20 questions, Mid-Level
- [Serde & Serialization](https://sharpskill.dev/en/technologies/rust/interview-questions/serde-serialization.md): 20 questions, Mid-Level
- [Unsafe Rust](https://sharpskill.dev/en/technologies/rust/interview-questions/unsafe-rust.md): 20 questions, Senior
- [Advanced Traits](https://sharpskill.dev/en/technologies/rust/interview-questions/advanced-traits.md): 22 questions, Senior
- [Advanced Lifetimes](https://sharpskill.dev/en/technologies/rust/interview-questions/advanced-lifetimes.md): 20 questions, Senior
- [Type System](https://sharpskill.dev/en/technologies/rust/interview-questions/type-system.md): 20 questions, Senior
- [Tokio & Async I/O](https://sharpskill.dev/en/technologies/rust/interview-questions/tokio-async.md): 22 questions, Senior
- [Performance Optimization](https://sharpskill.dev/en/technologies/rust/interview-questions/performance-optimization.md): 20 questions, Senior
- [Memory Management](https://sharpskill.dev/en/technologies/rust/interview-questions/memory-management.md): 20 questions, Senior
- [Web Frameworks](https://sharpskill.dev/en/technologies/rust/interview-questions/web-frameworks.md): 22 questions, Senior
- [Database Integration](https://sharpskill.dev/en/technologies/rust/interview-questions/database-integration.md): 20 questions, Senior
- [Rust Design Patterns](https://sharpskill.dev/en/technologies/rust/interview-questions/design-patterns.md): 20 questions, Senior

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