视频地址
头条地址：https://www.ixigua.com/i6775861706447913485
Ｂ站地址：https://www.bilibili.com/video/av81202308/
讲解内容
1、trait用于定义与其它类型共享的功能，类似于其它语言中的接口。
（1）可以通过trait以抽象的方式定义共享的行为。
（2）可以使用trait bounds指定泛型是任何拥有特定行为的类型。
2、定义trait
pub trait GetInformation{
fn get_name(&self) -> &String;
fn get_age(&self) -> u32;
}3、实现trait
//-----------------------------------------
pub struct Student {
pub name: String,
pub age: u32,
}
impl GetInformation for Student {
fn get_name(&self) -> &String {
&self.name
}
fn get_age(&self) -> u32 {
self.age
}
}
//----------------------------------------
pub struct Teacher {
pub name: String,
pub age: u32,
}
impl GetInformation for Teacher {
fn get_name(&self) -> &String {
&self.name
}
fn get_age(&self) -> u32 {
self.age
}
}
4、默认实现：可以在定义trait的时候提供默认的行为，trait的类型可以使用默认的行为。
例子：
trait SchoolName {
fn get_school_name(&self) -> String {
String::from("HongXingSchool")
}
}
//下面使用默认实现
pub struct Teacher {
pub name: String,
pub age: u32,
}
impl SchoolName for Teacher {}
fn main() {
let t = Teacher{ name: String::from("andy"), age: 32};
let t_school_name = t.get_school_name();
println!("teacher school name = {}", t_school_name);
}5、trait作为参数
例子：
pub fn print_information(item: impl GetInformation) {
println!("name = {}", item.get_name());
println!("age = {}", item.get_age());
}6、trait bound语法
上面的例子可以写成：
pub fn print_information<T: GetInformation>(item: T) {
println!("name = {}", item.get_name());
println!("age = {}", item.get_age());
}7、通过+指定多个trait bound
pub trait GetName {
fn get_name(&self) -> &String;
}
pub trait GetAge {
fn get_age(&self) -> u32;
}
//写法一
pub fn print_information<T: GetName+GetAge>(item: T) {
println!("name = {}", item.get_name());
println!("age = {}", item.get_age());
}
//写法二，使用where
pub fn print_information<T>(item: T)
where T: GetName+GetAge
{
println!("name = {}", item.get_name());
println!("age = {}", item.get_age());
}8、返回trait的类型
fn produce_item_with_information() -> impl GetInformation {
Teacher {
name: String::from("Andy"),
age: 32,
}
}但是，需要注意的是，只能返回单一类型，以下实现会出错（因为返回了两个类型）：
fn produce_item_with_information(is_teacher: bool) -> impl GetInformation {
if is_teacher {
Teacher {
name: String::from("Andy"),
age: 32,
}
} else {
Student {
name: String::from("harden"),
age: 47,
}
}
}9、复习之前的largest例子
fn largest<T：PartialOrd + Copy>(list: &[T]) -> T { //注意，要实现比较和复制的trait才行，否则报错
let mut largest = list[0];
for &item in list.iter() {
if item > largest {
largest = item;
}
}
largest
}
fn main(){
let number_list = vec![1, 2, 22, 3, 42];
let r1 = largest_i32(&number_list);
println!("r1 = {}", r1);
let char_list = vec!['a', 'y', 'c', 'd'];
let r2 = largest_char(&char_list);
println!("r2 = {}", r2);
}10、使用trait bound有条件地的实现方法
pub trait GetName {
fn get_name(&self) -> &String;
}
pub trait GetAge {
fn get_age(&self) -> u32;
}
struct PeopleMatchInformation<T, U> {
master: T,
employee: U,
}
impl <T: GetName+GetAge , U: GetName+GetAge> PeopleMatchInformation<T, U> {
fn print_all_information(&self) {
println!("teacher name = {}", self.master.get_name());
println!("teacher age = {}", self.master.get_age());
println!("student name = {}", self.employee.get_name());
println!("student age = {}", self.employee.get_age());
}
}
//使用
pub struct Teacher {
pub name: String,
pub age: u32,
}
impl GetName for Teacher {
fn get_name(&self) -> &String {
&(self.name)
}
}
impl GetAge for Teacher {
fn get_age(&self) -> u32{
self.age
}
}
pub struct Student{
pub name: String,
pub age: u32,
}
impl GetName for Student {
fn get_name(&self) -> &String {
&(self.name)
}
}
impl GetAge for Student {
fn get_age(&self) -> u32{
self.age
}
}
fn main() {
let t = Teacher{ name: String::from("andy"), age: 32};
let s = Student {name: String::from("harden"), age: 47};
let m = PeopleMatchInformation{master: t, employee: s};
m.print_all_information();
}11、对任何实现了特定trait的类型有条件的实现trait
例如：
pub trait GetName {
fn get_name(&self) -> &String;
}
pub trait PrintName {
fn print_name(&self) ;
}
impl<T: GetName> PrintName for T {
fn print_name(&self) {
println!("name = {}", self.get_name());
}
}
//----------使用----------------
pub struct Student{
pub name: String,
}
impl GetName for Student {
fn get_name(&self) -> &String {
&(self.name)
}
}
fn main() {
let s = Student{name: String::from("Andy")};
s.print_name(); //student实现了GetName trait，因此可是直接使用PrintName trait中的函数print_name
}
//引申：这种方式类似于c++里面的继承
