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 |
| } |
