actionbook/m15-anti-pattern
skills/m15-anti-pattern/SKILL.md
Use when reviewing code for anti-patterns. Keywords: anti-pattern, common mistake, pitfall, code smell, bad practice, code review, is this an anti-pattern, better way to do this, common mistake to avoid, why is this bad, idiomatic way, beginner mistake, fighting borrow checker, clone everywhere, unwrap in production, should I refactor, 反模式, 常见错误, 代码异味, 最佳实践, 地道写法
$ install --global
skillsauthnpx skillsauth add actionbook/rust-skills m15-anti-patternInstall this skill globally with one command. Works with Claude Code, Cursor, and Windsurf.
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SKILL.md
- name:
- m15-anti-pattern
- description:
- Use when reviewing code for anti-patterns. Keywords: anti-pattern, common mistake, pitfall, code smell, bad practice, code review, is this an anti-pattern, better way to do this, common mistake to avoid, why is this bad, idiomatic way, beginner mistake, fighting borrow checker, clone everywhere, unwrap in production, should I refactor, 反模式, 常见错误, 代码异味, 最佳实践, 地道写法
- user-invocable:
- false
Anti-Patterns
Layer 2: Design Choices
Core Question
Is this pattern hiding a design problem?
When reviewing code:
- Is this solving the symptom or the cause?
- Is there a more idiomatic approach?
- Does this fight or flow with Rust?
Anti-Pattern → Better Pattern
| Anti-Pattern | Why Bad | Better |
|--------------|---------|--------|
| .clone() everywhere | Hides ownership issues | Proper references or ownership |
| .unwrap() in production | Runtime panics | ?, expect, or handling |
| Rc when single owner | Unnecessary overhead | Simple ownership |
| unsafe for convenience | UB risk | Find safe pattern |
| OOP via Deref | Misleading API | Composition, traits |
| Giant match arms | Unmaintainable | Extract to methods |
| String everywhere | Allocation waste | &str, Cow<str> |
| Ignoring #[must_use] | Lost errors | Handle or let _ = |
Thinking Prompt
When seeing suspicious code:
-
Is this symptom or cause?
- Clone to avoid borrow? → Ownership design issue
- Unwrap "because it won't fail"? → Unhandled case
-
What would idiomatic code look like?
- References instead of clones
- Iterators instead of index loops
- Pattern matching instead of flags
-
Does this fight Rust?
- Fighting borrow checker → restructure
- Excessive unsafe → find safe pattern
Trace Up ↑
To design understanding:
"Why does my code have so many clones?"
↑ Ask: Is the ownership model correct?
↑ Check: m09-domain (data flow design)
↑ Check: m01-ownership (reference patterns)
| Anti-Pattern | Trace To | Question | |--------------|----------|----------| | Clone everywhere | m01-ownership | Who should own this data? | | Unwrap everywhere | m06-error-handling | What's the error strategy? | | Rc everywhere | m09-domain | Is ownership clear? | | Fighting lifetimes | m09-domain | Should data structure change? |
Trace Down ↓
To implementation (Layer 1):
"Replace clone with proper ownership"
↓ m01-ownership: Reference patterns
↓ m02-resource: Smart pointer if needed
"Replace unwrap with proper handling"
↓ m06-error-handling: ? operator
↓ m06-error-handling: expect with message
Top 5 Beginner Mistakes
| Rank | Mistake | Fix |
|------|---------|-----|
| 1 | Clone to escape borrow checker | Use references |
| 2 | Unwrap in production | Propagate with ? |
| 3 | String for everything | Use &str |
| 4 | Index loops | Use iterators |
| 5 | Fighting lifetimes | Restructure to own data |
Code Smell → Refactoring
| Smell | Indicates | Refactoring |
|-------|-----------|-------------|
| Many .clone() | Ownership unclear | Clarify data flow |
| Many .unwrap() | Error handling missing | Add proper handling |
| Many pub fields | Encapsulation broken | Private + accessors |
| Deep nesting | Complex logic | Extract methods |
| Long functions | Multiple responsibilities | Split |
| Giant enums | Missing abstraction | Trait + types |
Common Error Patterns
| Error | Anti-Pattern Cause | Fix | |-------|-------------------|-----| | E0382 use after move | Cloning vs ownership | Proper references | | Panic in production | Unwrap everywhere | ?, matching | | Slow performance | String for all text | &str, Cow | | Borrow checker fights | Wrong structure | Restructure | | Memory bloat | Rc/Arc everywhere | Simple ownership |
Deprecated → Better
| Deprecated | Better |
|------------|--------|
| Index-based loops | .iter(), .enumerate() |
| collect::<Vec<_>>() then iterate | Chain iterators |
| Manual unsafe cell | Cell, RefCell |
| mem::transmute for casts | as or TryFrom |
| Custom linked list | Vec, VecDeque |
| lazy_static! | std::sync::OnceLock |
Quick Review Checklist
- [ ] No
.clone()without justification - [ ] No
.unwrap()in library code - [ ] No
pubfields with invariants - [ ] No index loops when iterator works
- [ ] No
Stringwhere&strsuffices - [ ] No ignored
#[must_use]warnings - [ ] No
unsafewithout SAFETY comment - [ ] No giant functions (>50 lines)
Related Skills
| When | See | |------|-----| | Ownership patterns | m01-ownership | | Error handling | m06-error-handling | | Mental models | m14-mental-model | | Performance | m10-performance |
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