71 lines
1.7 KiB
Plaintext
71 lines
1.7 KiB
Plaintext
---
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title: Traits
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description: Defining shared behavior and contracts with Mist's signature ergonomics.
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icon: Sparkles
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---
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Traits in Mist define a set of methods that a type must implement, facilitating polymorphism and shared behavior. Method signatures use the `fn` keyword with `*self` for the instance parameter.
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## Defining a Trait
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A trait lists method signatures using `fn`, with `*self` as the instance parameter and the return type after the parameter list.
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```mist
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pub trait Drawable {
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fn draw(*self);
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fn metadata(*self) *str;
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}
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```
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## Implementing a Trait
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Use `impl Trait for Type` to provide implementations:
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```mist
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impl Drawable for Task {
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fn draw(*self) {
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println!("Drawing task: {}", self.name);
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}
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fn metadata(*self) *str {
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self.name
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}
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}
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```
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## Default Implementations
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Traits can provide default behavior for methods that implementing types may override:
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```mist
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pub trait Identifiable {
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fn get_id(*self) u32;
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fn is_valid(*self) bool {
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self.get_id() > 0
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}
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}
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```
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## Super-traits
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A trait can require another trait using the colon `:` syntax:
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```mist
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pub trait Speak {
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fn speak(*self) String;
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}
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pub trait Greet : Speak {
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fn greet(*self) String;
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}
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```
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## Key Characteristics
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- **`fn` Signatures**: Method signatures use `fn`, consistent with free functions.
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- **Explicit Context**: Methods use `*self` as the first parameter, mapping directly to Rust's reference rules.
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- **Default Methods**: Traits can provide default implementations.
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- **Super-traits**: Colon syntax for expressing trait requirements.
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- **Static Dispatch**: By default, Mist traits leverage Rust's zero-cost generics and monomorphization.
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