# Trait 与实现

URL: https://caijiao.org/rust/05-structure/03-traits
Source: docs/rust/05-structure/03-traits.md
Description: Trait 是 Rust 中定义共享行为的机制，类似接口，通过实现 Trait，类型可以拥有特定功能，实现多态。

Trait 定义一组方法签名，类型通过实现 Trait 获得对应行为。

## 定义 Trait

```rust
trait Summary {
    fn summarize(&self) -> String;
}
```

## 为结构体实现 Trait

```rust
struct NewsArticle {
    headline: String,
    author: String,
    content: String,
}

impl Summary for NewsArticle {
    fn summarize(&self) -> String {
        format!("{} by {}", self.headline, self.author)
    }
}
```

## 使用 Trait 对象多态

```rust
fn notify(item: &impl Summary) {
    println!("Breaking news! {}", item.summarize());
}

fn main() {
    let article = NewsArticle {
        headline: String::from("Rust 语言介绍"),
        author: String::from("张三"),
        content: String::from("Rust 是一种系统级编程语言。"),
    };
    notify(&article);
}
```

## Trait 约束泛型

```rust
fn notify_generic<T: Summary>(item: &T) {
    println!("News: {}", item.summarize());
}
```

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