rust trait

使用trait可以让不用的类型实现同一个行为,定义函数的默认实现.接口抽象,OOP范式抽象,函数式范式抽象均基于trait来完成.同时trait也保证了这些抽象几乎都是运行时零开销.

Rust一共提供了5个trait,都被定义在标准std::marker模块中.它们分别是
1.Sized trait:用来标识编译期中确定大小的类型
2.Unsized trait:实验特性?用来标识动态大小类型(DST)
3.Copy trait:用来标识可以按位复制其值的类型

#[derive(Copy,Clone)]
struct MyStruct;

4.Send trait:用来标识可以跨线程安全通信的类型,可以安全地在线程间传递值,也就是说可以跨线程传递所有权
5.Sync trait:用来标识可以在线程间共享引用的类型

Rust中冒号代表集合的"包含于"关系,而加号则代表交集
impl<T:A+B> C for T,为所有T(属于A和B的交集)实现Trait C

struct Person{
    name :&'static str,
    age:i32,
}

use std::fmt::*;
impl Debug for Person{
    fn fmt(&self,f:&mut Formatter) -> Result{
        write!(f," {{ name:{},age:{} }}",self.name,self.age)
    }
}

fn testTrait(){
    let p = Person{name:&"zs",age:20};
    println!("person:{:?}",p)
}

person: { name:zs,age:20 }

给i32实现Add

trait Add<T,Output> {
    fn add(self,t:T) -> Output;
}

impl Add<i32,i32> for i32{
    fn add(self,t:i32) -> i32{
        self + t
    }
}

impl Add<i32,u32> for u32{
    fn add(self,i:i32)-> u32{
        self + (i) as u32
    }
}

fn main() {
    let a:i32 = 1;
    let s = a.add(3);
    let u:u32 = 2;
    let s2 = u.add(4);
}

一个结构体实现2个trait

trait Page{
    fn set_page(&self,p:i32){
        println!("Page Default:{}",p);
    }
}

trait PerPage{
    fn set_perpage(&self,num:i32){
        println!("Per Page:{}",num);
    }
}

struct MyPage{
    page:i32,
}

impl Page for MyPage{}
impl PerPage for MyPage{}

fn testPage(){
    let p1 = MyPage{page:1};
    p1.set_page(2);
    p1.set_perpage(3);
}

Page Default:2
Per Page:3

pub trait Fly{
    fn fly(&self)->bool;
}

#[derive(Debug)]
struct Duck;
#[derive(Debug)]
struct Pig;

impl Fly for Duck{
    fn fly(&self)->bool{
        return true;
    }
}

impl Fly for Pig{
    fn fly(&self)->bool{
        return false;
    }
}

fn fly_static(s:impl Fly+Debug) -> bool{
    s.fly()
}

fn can_fly(s:impl Fly+Debug)->impl Fly{
    if s.fly(){
        println!("{:?} can fly",s);
    }else{
        println!("{:?} can't fly",s);
    }
    s
}

fn test_fly(){
    let pig = Pig;
    let pig = can_fly(pig);
    let d = Duck;
    if d.fly(){
        println!("{:?} can fly",d);
    }
}

Pig can't fly
Duck can fly