m15-anti-pattern
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
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/actionbook/rust-skills --skill m15-anti-pattern- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads m15-anti-pattern automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
Security audits
Independent scans of the skill's instructions and bundled files.
SKILL.md
The instructions your agent reads when the skill is triggered.
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 |
FAQ
What does the m15-anti-pattern skill do?
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
How do I install m15-anti-pattern?
Run npx skills add https://github.com/actionbook/rust-skills --skill m15-anti-pattern in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/m15-anti-pattern/ (personal) or .claude/skills/m15-anti-pattern/ (project).
Which AI agents can use m15-anti-pattern?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is m15-anti-pattern safe to install?
Security partners have reviewed it: Gen Agent Trust Hub passed; Socket passed; Snyk passed; Runlayer passed; ZeroLeaks passed. As with any skill, read the SKILL.md and bundled scripts before installing.
Who maintains m15-anti-pattern?
It is published by actionbook in actionbook/rust-skills. It has 8,652 recorded installs.
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