Traits & Interfaces

A trait defines a contract—a collection of method signatures that multiple structs or enums can implement to provide polymorphic behavior.

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Declaring a Trait

trait Describable {
    fn describe(&self) -> String
}

trait Drawable {
    fn draw(&self)
    fn area(&self) -> Float
}

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Implementing Traits for Types

Use impl Trait for Type to satisfy a trait interface:

struct Circle {
    radius: Float
}

impl Drawable for Circle {
    fn draw(&self) {
        print($"Drawing circle with radius {self.radius}")
    }

    fn area(&self) -> Float {
        return 3.14159 * self.radius * self.radius
    }
}

struct Rectangle {
    width: Float,
    height: Float
}

impl Drawable for Rectangle {
    fn draw(&self) {
        print($"Drawing rectangle {self.width}x{self.height}")
    }

    fn area(&self) -> Float {
        return self.width * self.height
    }
}

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Using Trait Polymorphism

You can write generic functions or receive traits as parameters:

fn render_shape(shape: &Drawable) {
    shape.draw()
    print($"Shape area: {shape.area()}")
}

let circle = Circle { radius: 5.0 }
let rect = Rectangle { width: 4.0, height: 6.0 }

render_shape(&circle)
render_shape(&rect)