trait 类似接口，定义了一组方法，struct可以实现trait

std trait

  1. struct Point {
  2.     x: i32,
  3.     y: i32,
  4. }
  6. impl Add for Point {
  7.     type Output = Self;
  9.     fn add(self, rhs: Self) -> Self::Output {
  10.         Point{
  11.             x: self.x + rhs.x,
  12.             y: self.y + rhs.y,
  13.         }
  14.     }
  15. }
  17. #[test]
  18. fn add_point() {
  19.     let p1 = Point {
  20.        x: 1,
  21.        y: 2,
  22.     };
  23.     let p2 = Point {
  24.        x: 1,
  25.        y: 2,
  26.     };
  27.     let p3 = p1 + p2;
  28.     assert_eq!(p3.x, 2);
  29.     assert_eq!(p3.y, 4);
  30. }
  1. fn write_to_buf(out: &mut Write) -> std::io::Result<()> {
  2.     out.write_all(b"hello world")?;
  3.     out.flush()
  4. }
  6.     #[test]
  7.     fn test_say_hello() {
  8.         let mut bytes: Vec<u8> = vec![];
  9.         let res = write_to_buf(&mut bytes);
  10.         assert_eq!(res.is_ok(), true);
  11.         assert_eq!(bytes, b"hello world");
  12.     }

custom trait

  1. trait NoisyAnimal {
  2.     fn make_noise(&self) -> &'static str;
  3. }
  5. struct Cat{}
  6. struct Dog{}
  8. impl NoisyAnimal for Cat {
  9.     fn make_noise(&self) -> &'static str {
  10.         "hello"
  11.     }
  12. }
  14. impl NoisyAnimal for Dog {
  15.     fn make_noise(&self) -> &'static str {
  16.         "bark"
  17.     }
  18. }
  20. fn main() {
  21.     let cat = Cat{};
  22.     println!("{}", cat.make_noise());
  23.     let dog = Dog{};
  24.     println!("{}", dog.make_noise());
  25. }

use trait as parameter

  1. fn make_noises(n: &impl NoisyAnimal) -> &'static str {
  2.     n.make_noise()
  3. }
  5. fn make_noises2<T>(n: &T) -> &'static str 
  6. where T: NoisyAnimal
  7. {
  8.     n.make_noise()
  9. }
  11. fn main() {
  12.     let cat = Cat{};
  13.     let dog = Dog{};
  14.     println!("{}", make_noises(&dog));
  15.     println!("{}", make_noises2(&cat));
  16. }

trait has no Size

  1. fn main() {
  2.     let cat = Cat{};
  3.     println!("{}", cat.make_noise());
  4.     let dog = Dog{};
  5.     println!("{}", dog.make_noise());
  7.     println!("{}", make_noises(&dog));
  8.     println!("{}", make_noises2(&cat));
  11.     let animals: Vec<Box<dyn NoisyAnimal>> = vec![Box::new(cat), Box::new(dog)];
  12.     for a in animals.iter() {
  13.         println!("{}", a.make_noise());
  14.     }
  15.     // 注意，这里cat，dog已经被move了，所以如果再次引用就会编译报错了
  16. }