rust - 如何在 Rust 的内部特征上实现外部特征？

Question

我想打印 的实例推特 主函数中的数据类型，但摘要特征不实现调试特征。有没有办法在 trait 上实现 trait 或任何解决方法。
取消注释第二行并注释第一行将起作用，因为 String 类型实现了 Display 特征。

#[derive(Debug)]
struct Tweet {
    name: String,
}

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

impl Summary for Tweet {
    fn summarize(&self) -> String {
        format!("@{}", &self.name)
    }
}

fn summarizeable(x: String) -> impl Summary {
    Tweet { name: x }
}

fn main() {
    //1.
    println!("{:#?}", summarizeable(String::from("Alex")));
    //2.println!("{}",summarizeable(String::from("Alex")).summarize());
}

error[E0277]: impl Summary doesn't implement std::fmt::Debug --> src/main.rs:26:29 | 26 | /1./ println!("{:#?}",summarizeable(String::from("Alex"))); |
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl Summary cannot be formatted using {:?} because it doesn't implement std::fmt::Debug | = help: the trait std::fmt::Debug is not implemented for impl Summary = note: required by std::fmt::Debug::fmt

error: aborting due to previous error

For more information about this error, try rustc --explain E0277. error: Could not compile p1.

To learn more, run the command again with --verbose.

Answer 1

您可以要求任何 impl小号 Summary还必须impl std::fmt::Debug如下:

pub trait Summary : std::fmt::Debug { // Summary requires Debug
    fn summarize(&self) -> String;
}

如果不想打结Debug至Summary您总是可以引入另一个包含其他两个特征的特征:

pub trait DebuggableSummary : Summary + std::fmt::Display {}