m01-ownership

What the source does

• FilesystemNone observedNo reads or writes in the source
• NetworkNone observedNo outbound calls in the source
• ShellNone observedNo commands run in the source
• DependenciesPinnedNothing floats
• SecretsNone foundNo keys in source

Five audit layers

Gates applied: no behavioural pass, no license.

Audit 0.4.1 · source sha f4ff8c82542d · 29 Oct 2026Report an issue or request a re-scan

• Publisheractionbook GitHub organizationOwner of the repository this skill is read from
• Source folderactionbook/rust-skills/skills/m01-ownershipThe exact folder we audited
• LicenceNot declaredAs the repository states it
• Commit pinned for this verdictf4ff8c82542dA new audit runs when the source changes
• Repository statusNot archivedLast push 66 days ago
• Sandboxed runNot runSkills are read, not executed; layer L4 is skipped

Its description: CRITICAL: Use for ownership/borrow/lifetime issues. Triggers: E0382, E0597, E0506, E0507, E0515, E0716, E0106, value moved, borrowed value does not live long enough, cannot move out of, use of moved value, ownership,…

---
name: m01-ownership
description: "CRITICAL: Use for ownership/borrow/lifetime issues. Triggers: E0382, E0597, E0506, E0507, E0515, E0716, E0106, value moved, borrowed value does not live long enough, cannot move out of, use of moved value, ownership, borrow, lifetime, 'a, 'static, move, clone, Copy, 所有权, 借用, 生命周期"
user-invocable: false
---

# Ownership & Lifetimes

> **Layer 1: Language Mechanics**

## Core Question

**Who should own this data, and for how long?**

Before fixing ownership errors, understand the data's role:
- Is it shared or exclusive?
- Is it short-lived or long-lived?
- Is it transformed or just read?

---

## Error → Design Question

| Error | Don't Just Say | Ask Instead |
|-------|----------------|-------------|
| E0382 | "Clone it" | Who should own this data? |
| E0597 | "Extend lifetime" | Is the scope boundary correct? |
| E0506 | "End borrow first" | Should mutation happen elsewhere? |
| E0507 | "Clone before move" | Why are we moving from a reference? |
| E0515 | "Return owned" | Should caller own the data? |
| E0716 | "Bind to variable" | Why is this temporary? |
| E0106 | "Add 'a" | What is the actual lifetime relationship? |

---

## Thinking Prompt

Before fixing an ownership error, ask:

1. **What is this data's domain role?**
   - Entity (unique identity) → owned
   - Value Object (interchangeable) → clone/copy OK
   - Temporary (computation result) → maybe restructure

2. **Is the ownership design intentional?**
   - By design → work within constraints
   - Accidental → consider redesign

3. **Fix symptom or redesign?**
   - If Strike 3 (3rd attempt) → escalate to Layer 2

---

## Trace Up ↑

When errors persist, trace to design layer:

```
E0382 (moved value)
    ↑ Ask: What design choice led to this ownership pattern?
    ↑ Check: m09-domain (is this Entity or Value Object?)
    ↑ Check: domain-* (what constraints apply?)
```

| Persistent Error | Trace To | Question |
|-----------------|----------|----------|
| E0382 repeated | m02-resource | Should use Arc/Rc for sharing? |
| E0597 repeated | m09-domain | Is scope boundary at right place? |
| E0506/E0507 | m03-mutability | Should use interior mutability? |

---

## Trace Down ↓

From design decisions to implementation:

```
"Data needs to be shared immutably"
    ↓ Use: Arc<T> (multi-thread) or Rc<T> (single-thread)

"Data needs exclusive ownership"
    ↓ Use: move semantics, take ownership

"Data is read-only view"
    ↓ Use: &T (immutable borrow)
```

---

## Quick Reference

| Pattern | Ownership | Cost | Use When |
|---------|-----------|------|----------|
| Move | Transfer | Zero | Caller doesn't need data |
| `&T` | Borrow | Zero | Read-only access |
| `&mut T` | Exclusive borrow | Zero | Need to modify |
| `clone()` | Duplicate | Alloc + copy | Actually need a copy |
| `Rc<T>` | Shared (single) | Ref count | Single-thread sharing |
| `Arc<T>` | Shared (multi) | Atomic ref count | Multi-thread sharing |
| `Cow<T>` | Clone-on-write | Alloc if mutated | Might modify |

## Error Code Reference

| Error | Cause | Quick Fix |
|-------|-------|-----------|
| E0382 | Value moved | Clone, reference, or redesign ownership |
| E0597 | Reference outlives owner | Extend owner scope or restructure |
| E0506 | Assign while borrowed | End borrow before mutation |
| E0507 | Move out of borrowed | Clone or use reference |
| E0515 | Return local reference | Return owned value |
| E0716 | Temporary dropped | Bind to variable |
| E0106 | Missing lifetime | Add `'a` annotation |

---

## Anti-Patterns

| Anti-Pattern | Why Bad | Better |
|--------------|---------|--------|
| `.clone()` everywhere | Hides design issues | Design ownership properly |
| Fight borrow checker | Increases complexity | Work with the compiler |
| `'static` for everything | Restricts flexibility | Use appropriate lifetimes |
| Leak with `Box::leak` | Memory leak | Proper lifetime design |

---

## Related Skills

| When | See |
|------|-----|
| Need smart pointers | m02-resource |
| Need interior mutability | m03-mutability |
| Data is domain entity | m09-domain |
| Learning ownership concepts | m14-mental-model |

Excerpt, first 4,140 characters of SKILL.md, verbatim from the audited commit. It is text from someone else’s repository, quoted so you can judge it before your agent reads it.

git clone https://github.com/actionbook/rust-skills
git -C rust-skills checkout f4ff8c82542d

Works in

1. 2026-10-29
   ✓SAFE B 89 / 100

   first audit · source f4ff8c82542d

Questions about m01-ownership

• github.com/actionbook/rust-skills/tree/main/skills/m01-ownership — the audited source at commit f4ff8c82542d and every finding aboveObserved · 29 Oct 2026

Spotted something wrong? Report a correction · Methodology