The 4 Horsemen of Bad Rust Code

In the right hands, Rust is an exceptionally powerful language. Yet, I frequently observe similar mistakes in Rust programming: treating it like C or Java and not fully utilizing its unique features.

I've concluded that poor Rust coding often falls into a few distinct categories, which I've termed the '4 Horsemen of Bad Rust Code': Overengineering, Simplistic Design, Premature Optimization, and Neglect of Documentation and Testing.

This talk will delve into these antipatterns and offer strategies to avoid them, aiming to share practical tips for writing more ergonomic and effective Rust code. During the talk, we will gradually refactor a Rust code example, transforming it from a less optimal version to a more idiomatic and efficient one.

Transcript

4. About me • Living in Düsseldorf, Germany • Backend engineer, open source maintainer, consultant at corrode.dev • Using Rust since 2015 • "Hello Rust" YouTube and "Rust in Production" Podcast
5. The Four Horsemen of Bad Rust Code Ignorance Excessive Abstraction Premature Optimization Omission
6. I. Ignorance
7. Ignorance • Uses "stringy-typed" APIs • Mutates liberally • Bad or no error handling • Lack of architecture • Prototype-style code
8. Ignorance: Red Flags • Imperative code • Magic return values (-1, "") instead of errors • Everything is a string • u nwr a p() • "c l on e () all the things!" • "mut"
9. Introducing the task
11. Rusty Rooms Residences;Brussels;2023-04-12;Deluxe;132.19 Ferris Motel One;Athens;2024-10-09;Family;227.43 Cargo Cabin;Oslo;2023-01-24;Double;170.17 Lifetime Lodge;Istanbul;2024-10-15;Family;177.94 Mutable Manor;Budapest;2023-03-26;Executive;197.24 Ownership Oasis;Prague;2024-11-07;Suite;77.94 Pattern Palace;Madrid;2023-03-17;Executive;195.5 Trait Towers;Amsterdam;2024-05-06;Double;141.94 Async Apartments;Rome;2023-06-28;Single;84.36 Binary Bungalows;Dublin;2024-05-01;Executive;146.57 Crates Cottage;Athens;2023-03-05;Suite;248.67 Data Den;Paris;2023-11-19;Single;238.3 Enum Estate;Berlin;2024-06-12;Double;277.98 Function Flat;Paris;2023-03-05;Double;277.88
12. Hotel Price in Brussels • Minimum: 40.13 • Mean: 80.42 • Maximum: 150.20 Expected Result:
14. 120 90 50 120 150 40 60 80 140
21. INDEX OUT OF BOUNDS?
22. INDEX OUT OF BOUNDS.
28. CSV is tricky... • Properly handling delimiters is hard. • h e l l o;r u st; f os d e m vs "h e l l o;r u st"; f os d e m • Encodings • Headlines? / No headlines? • etc. • Watch "Stop Using CSV"
39. Fighting Ignorance • Embrace Rust's type system • Lean into ownership and borrowing • Learn design patterns • Learn different programming paradigms
40. https://github.com/mre/idiomatic-rust
41. II. Excessive Abstraction
42. Excessive Abstraction • Over-Engineers solutions • Layers indirections • Excessive use of traits, generics, and lifetimes
43. Excessive Abstraction: Red Flags • "FileBuilder<T: AsRef<&str>, 'a>" • "I might use this again. Let's make it generic!" • "Traits! Traits everywhere!"
44. CSV JSON DATABASE
49. FN READ<'A>(&MUT SELF, READ: &'A MUT DYN READ) -> BOX<DYN ITERATOR<ITEM = RESULT<HOTEL>> + 'A>;
50. CSV JSON DATABASE
52. THOU SHALT HAVE NO NEED OF IT
53. MACROS COMPILE TIMES
54. Fighting Excessive Abstraction • Keep it simple • Avoid unnecessary complexity • Watch newcomers use your code • Ensure that abstractions add value
55. III. Premature Optimization
56. Premature Optimization • Optimizing code before it's necessary • Using complex data- structures where simple ones would suffice • Neglecting benchmarks
57. Premature Optimization: Red Flags • "Without a lifetime, this needs to be cloned!" • "Let me help the compiler here." • "Ooof, Box is so much overhead!" • "I use BTreeMap because it's faster than HashMap." • "No need to measure if you've got years of experience." • "Zero-copy abstraction" • "Alocaaaaations!!!"
58. clone()
63. CSV Parsing (deserialize) String object creation Floating Point operations HashMap access
64. E: Forgetting to run with --release
65. Find actual performance improvements • Measure! • Profile! •s u d o c a r g o f l a m e g r a ph --r e l e a s e • Benchmark! • criterion • divan
71. 34 seconds
72. 34 seconds
73. 32 seconds
75. 21 seconds
77. 13 seconds
79. 3.5 seconds
81. C Developer Rust Performance overhead!
83. Fighting Premature Optimization • Measure, don't guess. • Focus on algorithms and data structures, not micro- optimizations • You can get carried away quickly. Be more pragmatic. • Focus on readability and maintainability • Use profiling tools to make informed decisions
84. VI. Omission
85. Omission • Insufficient Testing • Lack of Documentation • Exposing too large APIs • Lack of modularity and encapsulation
86. Omission: Red Flags • "It compiles. My work is done here." • "The code is the documentation." • "Let's just make it all pub." • "I'll refactor that later."
91. Fighting Omission • Write more documentation • Write unit tests for your code • Use tools like clippy, cargo udeps, etc. • Set up CI/CD • Create releases • Keep a changelog
92. The Four Horsemen of Bad Rust Code Ignorance Excessive Abstraction Premature Optimization Omission
93. Further reading • RustFest Kiev 2017: Pascal Hertleif - Writing Idiomatic Libraries in Rust • FOSDEM 2018: Matthias Endler - Idiomatic Rust • EuroRust 2023: Nikolai Vazquez - Publishing High-Quality Crates
94. Thanks Illustr a tions by R a chel R a c a nelli a nd DALL·E 3
95. corrode.dev/idiomatic-rust