方法

方法是附着于对象的函数。这些方法通过self关键字访问对象的数据和它的其他方法。 方法是一个实现了impl块的定义。
 

struct Point {
    x: f64,
    y: f64,
}

// Implementation block, all `Point` methods go in here
impl Point {
    // This is a static method
    // Static methods don't need to be called by an instance
    // These methods are generally used as constructors
    fn origin() -> Point {
        Point { x: 0.0, y: 0.0 }
    }

    // Another static method, that takes two arguments
    fn new(x: f64, y: f64) -> Point {
        Point { x: x, y: y }
    }
}

struct Rectangle {
    p1: Point,
    p2: Point,
}

impl Rectangle {
    // This is an instance method
    // `&self` is sugar for `self: &Self`, where `Self` is the type of the
    // caller object. In this case `Self` = `Rectangle`
    fn area(&self) -> f64 {
        // `self` gives access to the struct fields via the dot operator
        let Point { x: x1, y: y1 } = self.p1;
        let Point { x: x2, y: y2 } = self.p2;

        // `abs` is a `f64` method that returns the absolute value of the
        // caller
        ((x1 - x2) * (y1 - y2)).abs()
    }

    fn perimeter(&self) -> f64 {
        let Point { x: x1, y: y1 } = self.p1;
        let Point { x: x2, y: y2 } = self.p2;

        2.0 * ((x1 - x2).abs() + (y1 - y2).abs())
    }

    // This method requires the caller object to be mutable
    // `&mut self` desugars to `self: &mut Self`
    fn translate(&mut self, x: f64, y: f64) {
        self.p1.x += x;
        self.p2.x += x;

        self.p1.y += y;
        self.p2.y += y;
    }
}

// `Pair` owns resources: two heap allocated integers
struct Pair(Box
 
  , Box
  
   ); impl Pair { // This method "consumes" the resources of the caller object // `self` desugars to `self: Self` fn destroy(self) { // Destructure `self` let Pair(first, second) = self; println!("Destroying Pair({}, {})", first, second); // `first` and `second` go out of scope and get freed } } fn main() { let rectangle = Rectangle { // Static methods are called using double colons p1: Point::origin(), p2: Point::new(3.0, 4.0), }; // Instance method are called using the dot operator // Note that the first argument `&self` is implicitly passed, i.e. // `rectangle.perimeter()` === `perimeter(&rectangle)` println!("Rectangle perimeter: {}", rectangle.perimeter()); println!("Rectangle area: {}", rectangle.area()); let mut square = Rectangle { p1: Point::origin(), p2: Point::new(1.0, 1.0), }; // Error! `rectangle` is immutable, but this method requires a mutable // object //rectangle.translate(1.0, 0.0); // TODO ^ Try uncommenting this line // Ok, mutable object can call mutable methods square.translate(1.0, 1.0); let pair = Pair(Box::new(1), Box::new(2)); pair.destroy(); // Error! Previous `destroy` call "consumed" `pair` //pair.destroy(); // TODO ^ Try uncommenting this line }