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关联类型 Associated Types

关联类型允许在 trait 中声明占位符类型，具体实现时确定，简化了复杂的泛型语法。

基本示例

rust 
trait Iterator {
    type Item;

    fn next(&mut self) -> Option<Self::Item>;
}

struct Counter {
    count: u32,
}

impl Iterator for Counter {
    type Item = u32;

    fn next(&mut self) -> Option<Self::Item> {
        self.count += 1;
        if self.count < 6 {
            Some(self.count)
        } else {
            None
        }
    }
}

fn main() {
    let mut counter = Counter { count: 0 };
    while let Some(num) = counter.next() {
        println!("计数器值: {}", num);
    }
}

代码演示

Rust Playground
打开运行 
trait Iterator {
    type Item;

fn next(&amp;mut self) -&gt; Option&lt;Self::Item&gt;;



}


struct Counter {
count: u32,
}


impl Iterator for Counter {
type Item = u32;


fn next(&amp;mut self) -&gt; Option&lt;Self::Item&gt; {
    self.count += 1;
    if self.count &lt; 6 {
        Some(self.count)
    } else {
        None
    }
}



}


fn main() {
let mut counter = Counter { count: 0 };
while let Some(num) = counter.next() {
println!("计数器值: {}", num);
}
}

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