Code Review in Rust: What to Check and How to Give Feedback for Beginners

Introduction: Why Code Review in Rust is Important for Beginners

Code review is one of the most effective ways to improve project quality and accelerate learning. For the Rust language, which is famous for its strict type system and unique ownership model, review becomes not just a formality, but a necessity. Beginner developers often make mistakes that the compiler does not catch, but which can lead to logical bugs or performance degradation.

In this article, we will break down what to pay attention to during a code review in Rust, how to give useful feedback, and how not to scare off a beginner with excessive criticism. The material will be useful both for those who are acting as a reviewer for the first time and for those who want to learn to write higher quality code.

1. Key Aspects to Check in Rust Code

A code review in Rust should cover several key areas. Below is a checklist for a beginner reviewer.

1.1. Ownership & Borrowing

This is the foundation of Rust. Even if the code compiles, it may contain excessive cloning or incorrect use of references. Check:

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• Is &str used instead of &String? (the latter is usually unnecessary)
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• Are there unnecessary .clone() calls? For example, if a function takes &T, there is no need to clone data before calling it.
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• Are borrowings used correctly: &mut T only when you need to modify data.
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// Bad: excessive cloning\nfn process(data: &Vec<String>) {\n    for item in data.clone() { // clone is not needed\n        println!("{}", item);\n    }\n}\n\n// Good: iterating by reference\nfn process(data: &[String]) {\n    for item in data {\n        println!("{}", item);\n    }\n}

1.2. Error Handling

Rust does not use exceptions, so proper error handling is critical. What to look for:

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• Are Result and Option used instead of panicking (.unwrap(), .expect())?
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• Is there error handling using match or the ? operator?
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• Is the error context lost? (it's useful to use map_err or custom error types)
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// Bad: panicking on error\nlet file = File::open("config.toml").unwrap();\n\n// Good: propagating the error with context\nfn read_config() -> Result<String, io::Error> {\n    let mut file = File::open("config.toml")?;\n    let mut contents = String::new();\n    file.read_to_string(&mut contents)?;\n    Ok(contents)\n}

1.3. Performance and Allocations

Beginners often don't think about unnecessary allocations. Pay attention to:

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• Using Vec where a fixed-size array ([T; N]) would suffice.
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• Creating strings with format! inside loops — it's better to collect them using join or push_str.
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• Premature optimization: don't criticize code for micro-allocations if it's not a hot path.
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2. How to Give Feedback: Gently, Specifically, and Constructively

Code review is not a competition, but a learning process. Your task is to help a colleague (or your future self) write better code, not to show how smart you are.

2.1. The "Sandwich" Rule (Praise-Criticism-Praise)

Start with something positive: note that the code is well-structured, or that the author correctly used match. Then point out the problem and suggest a solution. End with an encouraging phrase.

Example: "Great that you're using Option instead of panicking. One small note: here you could replace .unwrap() with ? to avoid a panic on error. Other than that, the code is excellent!"