Rust by Example: Traits

Traits are Rust's way of defining shared behavior between types. They are similar to interfaces or abstract base classes in other languages. A trait can be implemented for any type, and it can be used to define a set of methods that a type must have in order to be considered a member of that trait. This allows you to define shared behavior between types that are not related by inheritance.
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fn main() {

Define a trait named Shape with a method signature named area.

 
    trait Shape {
        fn area(&self) -> f64;
    }

Define two structs, Circle and Rectangle, that implement the Shape trait. Each struct has its own implementation of the area method.

 
    struct Circle {
        radius: f64,
    }

    impl Circle {
        fn new(radius: f64) -> Circle {
            Circle { radius }
        }
    }

Implement the Shape trait for the Circle struct.

 
    impl Shape for Circle {
        fn area(&self) -> f64 {
            3.4 * self.radius * self.radius
        }
    }

    struct Rectangle {
        width: f64,
        height: f64,
    }

    impl Rectangle {
        fn new(width: f64, height: f64) -> Rectangle {
            Rectangle { width, height }
        }
    }

Implement the Shape trait for the Rectangle struct.

 
    impl Shape for Rectangle {
        fn area(&self) -> f64 {
            self.width * self.height
        }
    }

Create instances of Circle and Rectangle and call their area methods.

 
    let circle = Circle::new(5.0);
    let rectangle = Rectangle::new(10.0, 20.0);

Define a function that takes a reference to a Shape trait object and calls its area method. This function can be used to print the area of any type that implements the Shape trait. &dyn Shape is a reference to a trait object that represents any type that implements the Shape trait.

 
    fn print_area(shape: &dyn Shape) {
        println!("Area: {}", shape.area());
    }

    print_area(&circle);
    print_area(&rectangle);
}

$ rustc traits.rs
$ ./traits
Area: 85
Area: 200
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