Mode d’emploi
- Copiez la commande et examinez le paquet avant de l’installer dans votre environnement agent.
- Consultez le document original pour les outils, identifiants et environnements requis.
- Décrivez les entrées et le livrable souhaité ; comparez la sortie aux sources.
npx skills add https://github.com/actionbook/rust-skills --skill m05-type-drivenAvant de commencer
- L’installation n’inclut ni abonnement au modèle, ni quota API, ni accès aux fichiers.
- Étoiles et installations reflètent l’activité, pas un test indépendant de qualité ou de sécurité.
Document Skill original
Rendu depuis le dépôt source en conservant titres, exemples, code, tableaux, liens et images.
Type-Driven Design
Layer 1: Language Mechanics
Core Question
How can the type system prevent invalid states?
Before reaching for runtime checks:
- Can the compiler catch this error?
- Can invalid states be unrepresentable?
- Can the type encode the invariant?
Error → Design Question
| Pattern | Don't Just Say | Ask Instead |
|---|---|---|
| Primitive obsession | "It's just a string" | What does this value represent? |
| Boolean flags | "Add an is_valid flag" | Can states be types? |
| Optional everywhere | "Check for None" | Is absence really possible? |
| Validation at runtime | "Return Err if invalid" | Can we validate at construction? |
Thinking Prompt
Before adding runtime validation:
- Can the type encode the constraint?
- Numeric range → bounded types or newtypes
- Valid states → type state pattern
- Semantic meaning → newtype
- When is validation possible?
- At construction → validated newtype
- At state transition → type state
- Only at runtime → Result with clear error
- Who needs to know the invariant?
- Compiler → type-level encoding
- API users → clear type signatures
- Runtime only → documentation
Trace Up ↑
When type design is unclear:
"Need to validate email format"
↑ Ask: Is this a domain value object?
↑ Check: m09-domain (Email as Value Object)
↑ Check: domain-* (validation requirements)| Situation | Trace To | Question |
|---|---|---|
| What types to create | m09-domain | What's the domain model? |
| State machine design | m09-domain | What are valid transitions? |
| Marker trait usage | m04-zero-cost | Static or dynamic dispatch? |
Trace Down ↓
From design to implementation:
"Need type-safe wrapper for primitives"
↓ Newtype: struct UserId(u64);
"Need compile-time state validation"
↓ Type State: Connection<Connected>
"Need to track phantom type parameters"
↓ PhantomData: PhantomData<T>
"Need capability markers"
↓ Marker Trait: trait Validated {}
"Need gradual construction"
↓ Builder: Builder::new().field(x).build()Quick Reference
| Pattern | Purpose | Example |
|---|---|---|
| Newtype | Type safety | struct UserId(u64); |
| Type State | State machine | Connection<Connected> |
| PhantomData | Variance/lifetime | PhantomData<&'a T> |
| Marker Trait | Capability flag | trait Validated {} |
| Builder | Gradual construction | Builder::new().name("x").build() |
| Sealed Trait | Prevent external impl | mod private { pub trait Sealed {} } |
Pattern Examples
Newtype
rust
struct Email(String); // Not just any string
impl Email {
pub fn new(s: &str) -> Result<Self, ValidationError> {
// Validate once, trust forever
validate_email(s)?;
Ok(Self(s.to_string()))
}
}Type State
rust
struct Connection<State>(TcpStream, PhantomData<State>);
struct Disconnected;
struct Connected;
struct Authenticated;
impl Connection<Disconnected> {
fn connect(self) -> Connection<Connected> { ... }
}
impl Connection<Connected> {
fn authenticate(self) -> Connection<Authenticated> { ... }
}Decision Guide
| Need | Pattern |
|---|---|
| Type safety for primitives | Newtype |
| Compile-time state validation | Type State |
| Lifetime/variance markers | PhantomData |
| Capability flags | Marker Trait |
| Gradual construction | Builder |
| Closed set of impls | Sealed Trait |
| Zero-sized type marker | ZST struct |
Anti-Patterns
| Anti-Pattern | Why Bad | Better |
|---|---|---|
| Boolean flags for states | Runtime errors | Type state |
| String for semantic types | No type safety | Newtype |
| Option for uninitialized | Unclear invariant | Builder |
| Public fields with invariants | Invariant violation | Private + validated new() |
Related Skills
| When | See |
|---|---|
| Domain modeling | m09-domain |
| Trait design | m04-zero-cost |
| Error handling in constructors | m06-error-handling |
| Anti-patterns | m15-anti-pattern |
