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npxskills add actionbook/rust-skills--skill m14-mental-modelLoading…
Layer 2: Design Choices
What's the right way to think about this Rust concept?
When learning or explaining Rust:
| Concept | Mental Model | Analogy |
|---|---|---|
| Ownership | Unique key | Only one person has the house key |
| Move | Key handover | Giving away your key |
&T | Lending for reading | Lending a book |
&mut T | Exclusive editing | Only you can edit the doc |
Lifetime 'a | Valid scope | "Ticket valid until..." |
Box<T> | Heap pointer | Remote control to TV |
Rc<T> | Shared ownership | Multiple remotes, last turns off |
Arc<T> | Thread-safe Rc | Remotes from any room |
| From | Key Shift |
|---|---|
| Java/C# | Values are owned, not references by default |
| C/C++ | Compiler enforces safety rules |
| Python/Go | No GC, deterministic destruction |
| Functional | Mutability is safe via ownership |
| JavaScript | No null, use Option instead |
When confused about Rust:
What's the ownership model?
What guarantee is Rust providing?
What's the compiler telling me?
To design understanding (Layer 2):
"Why can't I do X in Rust?"
↑ Ask: What safety guarantee would be violated?
↑ Check: m01-m07 for the rule being enforced
↑ Ask: What's the intended design pattern?
To implementation (Layer 1):
"I understand the concept, now how do I implement?"
↓ m01-ownership: Ownership patterns
↓ m02-resource: Smart pointer choice
↓ m07-concurrency: Thread safety
| Error | Wrong Model | Correct Model |
|---|---|---|
| E0382 use after move | GC cleans up | Ownership = unique key transfer |
| E0502 borrow conflict | Multiple writers OK | Only one writer at a time |
| E0499 multiple mut borrows | Aliased mutation | Exclusive access for mutation |
| E0106 missing lifetime | Ignoring scope | References have validity scope |
E0507 cannot move from &T | Implicit clone | References don't own data |
| Deprecated | Better |
|---|---|
| "Rust is like C++" | Different ownership model |
| "Lifetimes are GC" | Compile-time validity scope |
| "Clone solves everything" | Restructure ownership |
| "Fight the borrow checker" | Work with the compiler |
"unsafe to avoid rules" | Understand safe patterns first |
Stack Heap
+----------------+ +----------------+
| main() | | |
| s1 ─────────────────────> │ "hello" |
| | | |
| fn takes(s) { | | |
| s2 (moved) ─────────────> │ "hello" |
| } | | (s1 invalid) |
+----------------+ +----------------+
After move: s1 is no longer valid
+----------------+
| data: String |────────────> "hello"
+----------------+
↑
│ &data (immutable borrow)
│
+------+------+
| reader1 reader2 (multiple OK)
+------+------+
+----------------+
| data: String |────────────> "hello"
+----------------+
↑
│ &mut data (mutable borrow)
│
+------+
| writer (only one)
+------+
| Stage | Focus | Skills |
|---|---|---|
| Beginner | Ownership basics | m01-ownership, m14-mental-model |
| Intermediate | Smart pointers, error handling | m02, m06 |
| Advanced | Concurrency, unsafe | m07, unsafe-checker |
| Expert | Design patterns | m09-m15, domain-* |
| When | See |
|---|---|
| Ownership errors | m01-ownership |
| Smart pointers | m02-resource |
| Concurrency | m07-concurrency |
| Anti-patterns | m15-anti-pattern |
Create or update AgentSkills. Use when designing, structuring, or packaging skills with scripts, references, and assets.
Create or update AgentSkills. Use when designing, structuring, or packaging skills with scripts, references, and assets.
Use CodexBar CLI local cost usage to summarize per-model usage for Codex or Claude, including the current (most recent) model or a full model breakdown. Trigger when asked for model-level usage/cost data from codexbar, or when you need a scriptable per-model summary from codexbar cost JSON.
Set up and use 1Password CLI (op). Use when installing the CLI, enabling desktop app integration, signing in (single or multi-account), or reading/injecting/running secrets via op.
Create or update AgentSkills. Use when designing, structuring, or packaging skills with scripts, references, and assets.
Create or update AgentSkills. Use when designing, structuring, or packaging skills with scripts, references, and assets.
Use CodexBar CLI local cost usage to summarize per-model usage for Codex or Claude, including the current (most recent) model or a full model breakdown. Trigger when asked for model-level usage/cost data from codexbar, or when you need a scriptable per-model summary from codexbar cost JSON.
Set up and use 1Password CLI (op). Use when installing the CLI, enabling desktop app integration, signing in (single or multi-account), or reading/injecting/running secrets via op.