通过例子学习 Go 和 Rust ---- Interface 和 Trait

Go 的接口（interface）和 Rust 的特征（Trait）是经常被放在一起做比较的概念。咱可以用它们来实现计算不同几何形状的面积和周长的功能。

Go

type geometry interface {
    area() float64
    perim() float64
}

type rect struct {
    width, height float64
}
type circle struct {
    radius float64
}

func (r rect) area() float64 {
    return r.width * r.height
}
func (r rect) perim() float64 {
    return 2*r.width + 2*r.height
}

func (c circle) area() float64 {
    return math.Pi * c.radius * c.radius
}
func (c circle) perim() float64 {
    return 2 * math.Pi * c.radius
}


func measure(g geometry) {
    fmt.Println(g)
    fmt.Println(g.area())
    fmt.Println(g.perim())
}

func main() {
    r := rect{width: 3, height: 4}
    c := circle{radius: 5}
    
    measure(r)
    measure(c)
}

Rust

use core::f64::consts::PI;
use core::fmt::Debug;

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

#[derive(Debug)]
struct Rect {
    width: f64,
    height: f64,
}

#[derive(Debug)]
struct Circle {
    radius: f64,
}

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

    fn perim(&self) -> f64 {
        2.0 * self.height + 2.0 * self.width
    }
}

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

    fn perim(&self) -> f64 {
        2.0 * PI * self.radius
    }
}

fn main() {
    fn measure<T>(g: &T)
    where T: Geometry + Debug {
        println!("{:?}", g);
        println!("{:?}", g.area());
        println!("{:?}", g.perim());
    }
    
    let r = Rect{width: 3.0, height: 4.0};
    let c = Circle{radius: 5.0};
    
    measure(&r);
    measure(&c);
}