Rust方法

方法

方法是附着於對象的函數。這些方法通過self關鍵字訪問對象的數據和它的其他方法。 方法是一個實現了impl塊的定義。  

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 }

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