How to use
- Copy the installation command and review the source package before installing it in your own agent environment.
- Check the source document for required tools, credentials and supported hosts.
- Describe your input and desired deliverable; review the output against the source material.
npx skills add https://github.com/actionbook/rust-skills --skill m02-resourceBefore you start
- Installation does not include a model subscription, API allowance or permission to access your files.
- Repository stars and installation counts describe activity, not an independent quality or security test.
Original skill document
Rendered from the source repository. Headings, examples, code, tables, links, and referenced images are preserved.
Resource Management
Layer 1: Language Mechanics
Core Question
What ownership pattern does this resource need?
Before choosing a smart pointer, understand:
- Is ownership single or shared?
- Is access single-threaded or multi-threaded?
- Are there potential cycles?
Error → Design Question
| Error | Don't Just Say | Ask Instead |
|---|---|---|
| "Need heap allocation" | "Use Box" | Why can't this be on stack? |
| Rc memory leak | "Use Weak" | Is the cycle necessary in design? |
| RefCell panic | "Use try_borrow" | Is runtime check the right approach? |
| Arc overhead complaint | "Accept it" | Is multi-thread access actually needed? |
Thinking Prompt
Before choosing a smart pointer:
- What's the ownership model?
- Single owner → Box or owned value
- Shared ownership → Rc/Arc
- Weak reference → Weak
- What's the thread context?
- Single-thread → Rc, Cell, RefCell
- Multi-thread → Arc, Mutex, RwLock
- Are there cycles?
- Yes → One direction must be Weak
- No → Regular Rc/Arc is fine
Trace Up ↑
When pointer choice is unclear, trace to design:
"Should I use Arc or Rc?"
↑ Ask: Is this data shared across threads?
↑ Check: m07-concurrency (thread model)
↑ Check: domain-* (performance constraints)| Situation | Trace To | Question |
|---|---|---|
| Rc vs Arc confusion | m07-concurrency | What's the concurrency model? |
| RefCell panics | m03-mutability | Is interior mutability right here? |
| Memory leaks | m12-lifecycle | Where should cleanup happen? |
Trace Down ↓
From design to implementation:
"Need single-owner heap data"
↓ Use: Box<T>
"Need shared immutable data (single-thread)"
↓ Use: Rc<T>
"Need shared immutable data (multi-thread)"
↓ Use: Arc<T>
"Need to break reference cycle"
↓ Use: Weak<T>
"Need shared mutable data"
↓ Single-thread: Rc<RefCell<T>>
↓ Multi-thread: Arc<Mutex<T>> or Arc<RwLock<T>>Quick Reference
| Type | Ownership | Thread-Safe | Use When |
|---|---|---|---|
Box<T> | Single | Yes | Heap allocation, recursive types |
Rc<T> | Shared | No | Single-thread shared ownership |
Arc<T> | Shared | Yes | Multi-thread shared ownership |
Weak<T> | Weak ref | Same as Rc/Arc | Break reference cycles |
Cell<T> | Single | No | Interior mutability (Copy types) |
RefCell<T> | Single | No | Interior mutability (runtime check) |
Decision Flowchart
Need heap allocation?
├─ Yes → Single owner?
│ ├─ Yes → Box<T>
│ └─ No → Multi-thread?
│ ├─ Yes → Arc<T>
│ └─ No → Rc<T>
└─ No → Stack allocation (default)
Have reference cycles?
├─ Yes → Use Weak for one direction
└─ No → Regular Rc/Arc
Need interior mutability?
├─ Yes → Thread-safe needed?
│ ├─ Yes → Mutex<T> or RwLock<T>
│ └─ No → T: Copy? → Cell<T> : RefCell<T>
└─ No → Use &mut TCommon Errors
| Problem | Cause | Fix |
|---|---|---|
| Rc cycle leak | Mutual strong refs | Use Weak for one direction |
| RefCell panic | Borrow conflict at runtime | Use try_borrow or restructure |
| Arc overhead | Atomic ops in hot path | Consider Rc if single-threaded |
| Box unnecessary | Data fits on stack | Remove Box |
Anti-Patterns
| Anti-Pattern | Why Bad | Better |
|---|---|---|
| Arc everywhere | Unnecessary atomic overhead | Use Rc for single-thread |
| RefCell everywhere | Runtime panics | Design clear ownership |
| Box for small types | Unnecessary allocation | Stack allocation |
| Ignore Weak for cycles | Memory leaks | Design parent-child with Weak |
Related Skills
| When | See |
|---|---|
| Ownership errors | m01-ownership |
| Interior mutability details | m03-mutability |
| Multi-thread context | m07-concurrency |
| Resource lifecycle | m12-lifecycle |
