Agent skill

m14-mental-model

Use when learning Rust concepts. Keywords: mental model, how to think about ownership, understanding borrow checker, visualizing memory layout, analogy, misconception, explaining ownership, why does Rust, help me understand, confused about, learning Rust, explain like I'm, ELI5, intuition for, coming from Java, coming from Python, 心智模型, 如何理解所有权, 学习 Rust, Rust 入门, 为什么 Rust

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npx add-skill https://github.com/actionbook/rust-skills/tree/main/skills/m14-mental-model

SKILL.md

Mental Models

Layer 2: Design Choices

Core Question

What's the right way to think about this Rust concept?

When learning or explaining Rust:

  • What's the correct mental model?
  • What misconceptions should be avoided?
  • What analogies help understanding?

Key Mental Models

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

Coming From Other Languages

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

Thinking Prompt

When confused about Rust:

  1. What's the ownership model?

    • Who owns this data?
    • How long does it live?
    • Who can access it?
  2. What guarantee is Rust providing?

    • No data races
    • No dangling pointers
    • No use-after-free
  3. What's the compiler telling me?

    • Error = violation of safety rule
    • Solution = work with the rules

Trace Up ↑

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?

Trace Down ↓

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

Common Misconceptions

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 Thinking

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

Ownership Visualization

Stack                          Heap
+----------------+            +----------------+
| main()         |            |                |
|   s1 ─────────────────────> │ "hello"        |
|                |            |                |
| fn takes(s) {  |            |                |
|   s2 (moved) ─────────────> │ "hello"        |
| }              |            | (s1 invalid)   |
+----------------+            +----------------+

After move: s1 is no longer valid

Reference Visualization

+----------------+
| data: String   |────────────> "hello"
+----------------+
       ↑
       │ &data (immutable borrow)
       │
+------+------+
| reader1    reader2    (multiple OK)
+------+------+

+----------------+
| data: String   |────────────> "hello"
+----------------+
       ↑
       │ &mut data (mutable borrow)
       │
+------+
| writer (only one)
+------+

Learning Path

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-*

Related Skills

When See
Ownership errors m01-ownership
Smart pointers m02-resource
Concurrency m07-concurrency
Anti-patterns m15-anti-pattern

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