Anti-Patterns

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

actionbook/rust-skills·8Kinstalls1.5KstarsCode Review & Quality

SKILL.md

Full skill instructions

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 pub fields with invariants
No index loops when iterator works
No String where &str suffices
No ignored #[must_use] warnings
No unsafe without 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

Install skill

Copy and run in your terminal

npx -y skills add https://github.com/actionbook/rust-skills --skill m15-anti-pattern

View on GitHub

m15-anti-pattern

More Code Review & Quality skills

View all

Code Review & Quality

azure-enterprise-infra-planner

Enterprise Azure infrastructure architect generating Bicep or Terraform from workload descriptions.

1.5K 454.3K

View

Code Review & Quality

caveman-review

Ultra-compressed code review comments: location, problem, fix on one line each.

109.9K 388.8K

View

Code Review & Quality

requesting-code-review

Dispatch code review subagents with focused context to catch issues before they compound.

295.4K 245.8K

View

Code Review & Quality

executing-plans

Execute a written implementation plan with critical review and task checkpoints.

295.4K 229.1K

View

Code Review & Quality

subagent-driven-development

Dispatch fresh subagents per task with two-stage review (spec compliance, then code quality) in the current session.

295.4K 221.7K

View

Code Review & Quality

seo-audit

Comprehensive SEO auditing framework covering crawlability, indexation, speed, on-page optimization, and content quality.

53.3K 220.8K

View

Code Review & Quality

receiving-code-review

Evaluate code review feedback with technical rigor before implementing, avoiding performative agreement and blind implementation.

295.4K 208.8K

View

Code Review & Quality

gpt-image-2

Generate images via your ChatGPT subscription using text-to-image, image editing, and style transfer.

16 169.5K

View

Code Review & Quality

mcp-builder

Guide for creating high-quality MCP (Model Context Protocol) servers that enable LLMs to interact with external services through well-designed tools. Use when building MCP servers to integrate external APIs or services, whether in Python (FastMCP) or Node/TypeScript (MCP SDK).

179.7K 122.7K

View

Code Review & Quality