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< h1 id = "深入了解特征" > < a class = "header" href = "#深入了解特征" > 深入了解特征< / a > < / h1 >
< p > 特征之于 Rust 更甚于接口之于其他语言，因此特征在 Rust 中很重要也相对较为复杂，我们决定把特征分为两篇进行介绍，< a href = "https://course.rs/basic/trait/trait.html" > 第一篇< / a > 在之前已经讲过，现在就是第二篇：关于特征的进阶篇，会讲述一些不常用到但是你该了解的特性。< / p >
< h2 id = "关联类型" > < a class = "header" href = "#关联类型" > 关联类型< / a > < / h2 >
< p > 在方法一章中，我们讲到了< a href = "https://course.rs/basic/method#关联函数" > 关联函数< / a > ，但是实际上关联类型和关联函数并没有任何交集，虽然它们的名字有一半的交集。< / p >
< p > 关联类型是在特征定义的语句块中，声明一个自定义类型，这样就可以在特征的方法签名中使用该类型：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > pub trait Iterator {
type Item;
fn next(& mut self) -> Option< Self::Item> ;
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 以上是标准库中的迭代器特征 < code > Iterator< / code > ，它有一个 < code > Item< / code > 关联类型，用于替代遍历的值的类型。< / p >
< p > 同时，< code > next< / code > 方法也返回了一个 < code > Item< / code > 类型，不过使用 < code > Option< / code > 枚举进行了包裹，假如迭代器中的值是 < code > i32< / code > 类型，那么调用 < code > next< / code > 方法就将获取一个 < code > Option< i32> < / code > 的值。< / p >
< p > 还记得 < code > Self< / code > 吧？在之前的章节< a href = "https://course.rs/basic/trait/trait-object#self-与-self" > 提到过< / a > ， < strong > < code > Self< / code > 用来指代当前调用者的具体类型，那么 < code > Self::Item< / code > 就用来指代该类型实现中定义的 < code > Item< / code > 类型< / strong > ： < / p >
< pre class = "playground" > < code class = "language-rust edition2021" > impl Iterator for Counter {
type Item = u32;
fn next(& mut self) -> Option< Self::Item> {
// --snip--
}
}
fn main() {
let c = Counter{..}
c.next()
}< / code > < / pre >
< p > 在上述代码中，我们为 < code > Counter< / code > 类型实现了 < code > Iterator< / code > 特征，变量 < code > c< / code > 是特征 < code > Iterator< / code > 的实例，也是 < code > next< / code > 方法的调用者。 结合之前的黑体内容可以得出：对于 < code > next< / code > 方法而言，< code > Self< / code > 是调用者 < code > c< / code > 的具体类型： < code > Counter< / code > ，而 < code > Self::Item< / code > 是 < code > Counter< / code > 中定义的 < code > Item< / code > 类型: < code > u32< / code > 。< / p >
< p > 聪明的读者之所以聪明，是因为你们喜欢联想和举一反三，同时你们也喜欢提问：为何不用泛型，例如如下代码：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > pub trait Iterator< Item> {
fn next(& mut self) -> Option< Item> ;
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 答案其实很简单，为了代码的可读性，当你使用了泛型后，你需要在所有地方都写 < code > Iterator< Item> < / code > ，而使用了关联类型，你只需要写 < code > Iterator< / code > ，当类型定义复杂时，这种写法可以极大的增加可读性：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > pub trait CacheableItem: Clone + Default + fmt::Debug + Decodable + Encodable {
type Address: AsRef< [u8]> + Clone + fmt::Debug + Eq + Hash;
fn is_null(& self) -> bool;
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 例如上面的代码，< code > Address< / code > 的写法自然远比 < code > AsRef< [u8]> + Clone + fmt::Debug + Eq + Hash< / code > 要简单的多，而且含义清晰。< / p >
< p > 再例如，如果使用泛型，你将得到以下的代码：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > trait Container< A,B> {
fn contains(& self,a: A,b: B) -> bool;
}
fn difference< A,B,C> (container: & C) -> i32
where
C : Container< A,B> {...}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 可以看到，由于使用了泛型，导致函数头部也必须增加泛型的声明，而使用关联类型，将得到可读性好得多的代码：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > trait Container{
type A;
type B;
fn contains(& self, a: & Self::A, b: & Self::B) -> bool;
}
fn difference< C: Container> (container: & C) {}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 关联类型还可以被其它特征进行约束，例如：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > trait Container{
type A: Display;
type B;
fn contains(& self, a: & Self::A, b: & Self::B) -> bool;
}
< span class = "boring" > }< / span > < / code > < / pre >
< h2 id = "默认泛型类型参数" > < a class = "header" href = "#默认泛型类型参数" > 默认泛型类型参数< / a > < / h2 >
< p > 当使用泛型类型参数时，可以为其指定一个默认的具体类型，例如标准库中的 < code > std::ops::Add< / code > 特征：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > trait Add< RHS=Self> {
type Output;
fn add(self, rhs: RHS) -> Self::Output;
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 它有一个泛型参数 < code > RHS< / code > ，但是与我们以往的用法不同，这里它给 < code > RHS< / code > 一个默认值，也就是当用户不指定 < code > RHS< / code > 时，默认使用两个同样类型的值进行相加，然后返回一个关联类型 < code > Output< / code > 。< / p >
< p > 可能上面那段不太好理解，下面我们用代码来举例：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > use std::ops::Add;
#[derive(Debug, PartialEq)]
struct Point {
x: i32,
y: i32,
}
impl Add for Point {
type Output = Point;
fn add(self, other: Point) -> Point {
Point {
x: self.x + other.x,
y: self.y + other.y,
}
}
}
fn main() {
assert_eq!(Point { x: 1, y: 0 } + Point { x: 2, y: 3 },
Point { x: 3, y: 3 });
}< / code > < / pre >
< p > 上面的代码主要干了一件事，就是为 < code > Point< / code > 结构体提供 < code > +< / code > 的能力，这就是< strong > 运算符重载< / strong > ，不过 Rust 并不支持创建自定义运算符，你也无法为所有运算符进行重载，目前来说，只有定义在 < code > std::ops< / code > 中的运算符才能进行重载。< / p >
< p > 跟 < code > +< / code > 对应的特征是 < code > std::ops::Add< / code > ，我们在之前也看过它的定义 < code > trait Add< RHS=Self> < / code > ，但是上面的例子中并没有为 < code > Point< / code > 实现 < code > Add< RHS> < / code > 特征，而是实现了 < code > Add< / code > 特征（没有默认泛型类型参数），这意味着我们使用了 < code > RHS< / code > 的默认类型，也就是 < code > Self< / code > 。换句话说，我们这里定义的是两个相同的 < code > Point< / code > 类型相加，因此无需指定 < code > RHS< / code > 。< / p >
< p > 与上面的例子相反，下面的例子，我们来创建两个不同类型的相加：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > use std::ops::Add;
struct Millimeters(u32);
struct Meters(u32);
impl Add< Meters> for Millimeters {
type Output = Millimeters;
fn add(self, other: Meters) -> Millimeters {
Millimeters(self.0 + (other.0 * 1000))
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 这里，是进行 < code > Millimeters + Meters< / code > 两种数据类型的 < code > +< / code > 操作，因此此时不能再使用默认的 < code > RHS< / code > ，否则就会变成 < code > Millimeters + Millimeters< / code > 的形式。使用 < code > Add< Meters> < / code > 可以将 < code > RHS< / code > 指定为 < code > Meters< / code > ，那么 < code > fn add(self, rhs: RHS)< / code > 自然而言的变成了 < code > Millimeters< / code > 和 < code > Meters< / code > 的相加。< / p >
< p > 默认类型参数主要用于两个方面：< / p >
< ol >
< li > 减少实现的样板代码< / li >
< li > 扩展类型但是无需大幅修改现有的代码< / li >
< / ol >
< p > 之前的例子就是第一点，虽然效果也就那样。在 < code > +< / code > 左右两边都是同样类型时，只需要 < code > impl Add< / code > 即可，否则你需要 < code > impl Add< SOME_TYPE> < / code > ，嗯，会多写几个字:)< / p >
< p > 对于第二点，也很好理解，如果你在一个复杂类型的基础上，新引入一个泛型参数，可能需要修改很多地方，但是如果新引入的泛型参数有了默认类型，情况就会好很多，添加泛型参数后，使用这个类型的代码需要逐个在类型提示部分添加泛型参数，就很麻烦；但是有了默认参数（且默认参数取之前的实现里假设的值的情况下）之后，原有的使用这个类型的代码就不需要做改动了。< / p >
< p > 归根到底，默认泛型参数，是有用的，但是大多数情况下，咱们确实用不到，当需要用到时，大家再回头来查阅本章即可，< strong > 手上有剑，心中不慌< / strong > 。< / p >
< h2 id = "调用同名的方法" > < a class = "header" href = "#调用同名的方法" > 调用同名的方法< / a > < / h2 >
< p > 不同特征拥有同名的方法是很正常的事情，你没有任何办法阻止这一点；甚至除了特征上的同名方法外，在你的类型上，也有同名方法：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > trait Pilot {
fn fly(& self);
}
trait Wizard {
fn fly(& self);
}
struct Human;
impl Pilot for Human {
fn fly(& self) {
println!("This is your captain speaking.");
}
}
impl Wizard for Human {
fn fly(& self) {
println!("Up!");
}
}
impl Human {
fn fly(& self) {
println!("*waving arms furiously*");
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 这里，不仅仅两个特征 < code > Pilot< / code > 和 < code > Wizard< / code > 有 < code > fly< / code > 方法，就连实现那两个特征的 < code > Human< / code > 单元结构体，也拥有一个同名方法 < code > fly< / code > (这世界怎么了，非要这么卷吗？程序员何苦难为程序员，哎)。< / p >
< p > 既然代码已经不可更改，那下面我们来讲讲该如何调用这些 < code > fly< / code > 方法。< / p >
< h4 id = "优先调用类型上的方法" > < a class = "header" href = "#优先调用类型上的方法" > 优先调用类型上的方法< / a > < / h4 >
< p > 当调用 < code > Human< / code > 实例的 < code > fly< / code > 时，编译器默认调用该类型中定义的方法：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
let person = Human;
person.fly();
}< / code > < / pre >
< p > 这段代码会打印 < code > *waving arms furiously*< / code > ，说明直接调用了类型上定义的方法。< / p >
< h4 id = "调用特征上的方法" > < a class = "header" href = "#调用特征上的方法" > 调用特征上的方法< / a > < / h4 >
< p > 为了能够调用两个特征的方法，需要使用显式调用的语法：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
let person = Human;
Pilot::fly(& person); // 调用Pilot特征上的方法
Wizard::fly(& person); // 调用Wizard特征上的方法
person.fly(); // 调用Human类型自身的方法
}< / code > < / pre >
< p > 运行后依次输出：< / p >
< pre > < code class = "language-console" > This is your captain speaking.
Up!
*waving arms furiously*
< / code > < / pre >
< p > 因为 < code > fly< / code > 方法的参数是 < code > self< / code > ，当显式调用时，编译器就可以根据调用的类型( < code > self< / code > 的类型)决定具体调用哪个方法。< / p >
< p > 这个时候问题又来了，如果方法没有 < code > self< / code > 参数呢？稍等，估计有读者会问：还有方法没有 < code > self< / code > 参数？看到这个疑问，作者的眼泪不禁流了下来，大明湖畔的< a href = "https://course.rs/basic/method.html#关联函数" > 关联函数< / a > ，你还记得嘛？< / p >
< p > 但是成年人的世界，就算再伤心，事还得做，咱们继续：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > trait Animal {
fn baby_name() -> String;
}
struct Dog;
impl Dog {
fn baby_name() -> String {
String::from("Spot")
}
}
impl Animal for Dog {
fn baby_name() -> String {
String::from("puppy")
}
}
fn main() {
println!("A baby dog is called a {}", Dog::baby_name());
}< / code > < / pre >
< p > 就像人类妈妈会给自己的宝宝起爱称一样，狗妈妈也会。狗妈妈称呼自己的宝宝为< strong > Spot< / strong > ，其它动物称呼狗宝宝为< strong > puppy< / strong > ，这个时候假如有动物不知道该如何称呼狗宝宝，它需要查询一下。< / p >
< p > < code > Dog::baby_name()< / code > 的调用方式显然不行，因为这只是狗妈妈对宝宝的爱称，可能你会想到通过下面的方式查询其他动物对狗狗的称呼：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
println!("A baby dog is called a {}", Animal::baby_name());
}< / code > < / pre >
< p > 铛铛，无情报错了：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > error[E0283]: type annotations needed // 需要类型注释
--> src/main.rs:20:43
|
20 | println!("A baby dog is called a {}", Animal::baby_name());
| ^^^^^^^^^^^^^^^^^ cannot infer type // 无法推断类型
|
= note: cannot satisfy `_: Animal`
< span class = "boring" > }< / span > < / code > < / pre >
< p > 因为单纯从 < code > Animal::baby_name()< / code > 上，编译器无法得到任何有效的信息：实现 < code > Animal< / code > 特征的类型可能有很多，你究竟是想获取哪个动物宝宝的名称？狗宝宝？猪宝宝？还是熊宝宝？< / p >
< p > 此时，就需要使用< strong > 完全限定语法< / strong > 。< / p >
< h5 id = "完全限定语法" > < a class = "header" href = "#完全限定语法" > 完全限定语法< / a > < / h5 >
< p > 完全限定语法是调用函数最为明确的方式：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
println!("A baby dog is called a {}", < Dog as Animal> ::baby_name());
}< / code > < / pre >
< p > 在尖括号中，通过 < code > as< / code > 关键字，我们向 Rust 编译器提供了类型注解，也就是 < code > Animal< / code > 就是 < code > Dog< / code > ，而不是其他动物，因此最终会调用 < code > impl Animal for Dog< / code > 中的方法，获取到其它动物对狗宝宝的称呼：< strong > puppy< / strong > 。< / p >
< p > 言归正题，完全限定语法定义为：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > < Type as Trait> ::function(receiver_if_method, next_arg, ...);
< span class = "boring" > }< / span > < / code > < / pre >
< p > 上面定义中，第一个参数是方法接收器 < code > receiver< / code > （三种 < code > self< / code > ），只有方法才拥有，例如关联函数就没有 < code > receiver< / code > 。< / p >
< p > 完全限定语法可以用于任何函数或方法调用，那么我们为何很少用到这个语法？原因是 Rust 编译器能根据上下文自动推导出调用的路径，因此大多数时候，我们都无需使用完全限定语法。只有当存在多个同名函数或方法，且 Rust 无法区分出你想调用的目标函数时，该用法才能真正有用武之地。< / p >
< h2 id = "特征定义中的特征约束" > < a class = "header" href = "#特征定义中的特征约束" > 特征定义中的特征约束< / a > < / h2 >
< p > 有时，我们会需要让某个特征 A 能使用另一个特征 B 的功能(另一种形式的特征约束)，这种情况下，不仅仅要为类型实现特征 A， < / p >
< p > 例如有一个特征 < code > OutlinePrint< / code > ，它有一个方法，能够对当前的实现类型进行格式化输出：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > use std::fmt::Display;
trait OutlinePrint: Display {
fn outline_print(& self) {
let output = self.to_string();
let len = output.len();
println!("{}", "*".repeat(len + 4));
println!("*{}*", " ".repeat(len + 2));
println!("* {} *", output);
println!("*{}*", " ".repeat(len + 2));
println!("{}", "*".repeat(len + 4));
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 等等，这里有一个眼熟的语法: < code > OutlinePrint: Display< / code > ，感觉很像之前讲过的< strong > 特征约束< / strong > ，只不过用在了特征定义中而不是函数的参数中，是的，在某种意义上来说，这和特征约束非常类似，都用来说明一个特征需要实现另一个特征，这里就是：如果你想要实现 < code > OutlinePrint< / code > 特征，首先你需要实现 < code > Display< / code > 特征。< / p >
< p > 想象一下，假如没有这个特征约束，那么 < code > self.to_string< / code > 还能够调用吗（ < code > to_string< / code > 方法会为实现 < code > Display< / code > 特征的类型自动实现）？编译器肯定是不愿意的，会报错说当前作用域中找不到用于 < code > & Self< / code > 类型的方法 < code > to_string< / code > ： < / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > struct Point {
x: i32,
y: i32,
}
impl OutlinePrint for Point {}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 因为 < code > Point< / code > 没有实现 < code > Display< / code > 特征，会得到下面的报错：< / p >
< pre > < code class = "language-console" > error[E0277]: the trait bound `Point: std::fmt::Display` is not satisfied
--> src/main.rs:20:6
|
20 | impl OutlinePrint for Point {}
| ^^^^^^^^^^^^ `Point` cannot be formatted with the default formatter;
try using `:?` instead if you are using a format string
|
= help: the trait `std::fmt::Display` is not implemented for `Point`
< / code > < / pre >
< p > 既然我们有求于编译器，那只能选择满足它咯：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > use std::fmt;
impl fmt::Display for Point {
fn fmt(& self, f: & mut fmt::Formatter) -> fmt::Result {
write!(f, "({}, {})", self.x, self.y)
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 上面代码为 < code > Point< / code > 实现了 < code > Display< / code > 特征，那么 < code > to_string< / code > 方法也将自动实现：最终获得字符串是通过这里的 < code > fmt< / code > 方法获得的。< / p >
< h2 id = "在外部类型上实现外部特征newtype" > < a class = "header" href = "#在外部类型上实现外部特征newtype" > 在外部类型上实现外部特征(newtype)< / a > < / h2 >
< p > 在< a href = "https://course.rs/basic/trait/trait#特征定义与实现的位置孤儿规则" > 特征< / a > 章节中，有提到孤儿规则，简单来说，就是特征或者类型必需至少有一个是本地的，才能在此类型上定义特征。< / p >
< p > 这里提供一个办法来绕过孤儿规则，那就是使用< strong > newtype 模式< / strong > ，简而言之：就是为一个< a href = "https://course.rs/basic/compound-type/struct#元组结构体tuple-struct" > 元组结构体< / a > 创建新类型。该元组结构体封装有一个字段，该字段就是希望实现特征的具体类型。< / p >
< p > 该封装类型是本地的，因此我们可以为此类型实现外部的特征。< / p >
< p > < code > newtype< / code > 不仅仅能实现以上的功能，而且它在运行时没有任何性能损耗，因为在编译期，该类型会被自动忽略。< / p >
< p > 下面来看一个例子，我们有一个动态数组类型： < code > Vec< T> < / code > ，它定义在标准库中，还有一个特征 < code > Display< / code > ，它也定义在标准库中，如果没有 < code > newtype< / code > ，我们是无法为 < code > Vec< T> < / code > 实现 < code > Display< / code > 的：< / p >
< pre > < code class = "language-console" > error[E0117]: only traits defined in the current crate can be implemented for arbitrary types
--> src/main.rs:5:1
|
5 | impl< T> std::fmt::Display for Vec< T> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^------
| | |
| | Vec is not defined in the current crate
| impl doesn't use only types from inside the current crate
|
= note: define and implement a trait or new type instead
< / code > < / pre >
< p > 编译器给了我们提示： < code > define and implement a trait or new type instead< / code > ，重新定义一个特征，或者使用 < code > new type< / code > ，前者当然不可行，那么来试试后者：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > use std::fmt;
struct Wrapper(Vec< String> );
impl fmt::Display for Wrapper {
fn fmt(& self, f: & mut fmt::Formatter) -> fmt::Result {
write!(f, "[{}]", self.0.join(", "))
}
}
fn main() {
let w = Wrapper(vec![String::from("hello"), String::from("world")]);
println!("w = {}", w);
}< / code > < / pre >
< p > 其中，< code > struct Wrapper(Vec< String> )< / code > 就是一个元组结构体，它定义了一个新类型 < code > Wrapper< / code > ，代码很简单，相信大家也很容易看懂。< / p >
< p > 既然 < code > new type< / code > 有这么多好处，它有没有不好的地方呢？答案是肯定的。注意到我们怎么访问里面的数组吗？< code > self.0.join(", ")< / code > ，是的，很啰嗦，因为需要先从 < code > Wrapper< / code > 中取出数组: < code > self.0< / code > ，然后才能执行 < code > join< / code > 方法。< / p >
< p > 类似的，任何数组上的方法，你都无法直接调用，需要先用 < code > self.0< / code > 取出数组，然后再进行调用。< / p >
< p > 当然，解决办法还是有的，要不怎么说 Rust 是极其强大灵活的编程语言！ < a href = "https://course.rs/advance/smart-pointer/deref.html" > < code > Deref< / code > < / a > ，实现该特征后，可以自动做一层类似类型转换的操作，可以将 < code > Wrapper< / code > 变成 < code > Vec< String> < / code > 来使用。这样就会像直接使用数组那样去使用 < code > Wrapper< / code > ，而无需为每一个操作都添加上 < code > self.0< / code > 。< / p >
< p > 同时，如果不想 < code > Wrapper< / code > 暴露底层数组的所有方法，我们还可以为 < code > Wrapper< / code > 去重载这些方法，实现隐藏的目的。< / p >
< h2 id = "课后练习" > < a class = "header" href = "#课后练习" > 课后练习< / a > < / h2 >
< blockquote >
< p > < a href = "https://practice-zh.course.rs/generics-traits/advanced-traits.html" > Rust By Practice< / a > ，支持代码在线编辑和运行，并提供详细的< a href = "https://github.com/sunface/rust-by-practice/blob/master/solutions/generics-traits/advanced-trait.md" > 习题解答< / a > 。< / p >
< / blockquote >
< / main >
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