rust - 如何在其多态类型上调用 Display 特征？

Question

我有:

use std::fmt;
struct TeamMember {
    name: String,
    age: u32,
}

struct Manager {
    name: String,
    age: u32,
}

impl fmt::Display for TeamMember {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { 
         write!(f, "TeamMember; name => {}, age => {}", self.name, self.age)
      }
}

impl fmt::Display for Manager {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { 
         write!(f, "Manager; name => {}, age => {}", self.name, self.age)
      }
}

trait Employee {}

impl fmt::Display for Employee {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { 
         write!(f, "{}", *self)
      }
}

fn main() {
    let t = TeamMember { name: "abc".to_string(), age: 23 };
    let t2 = Manager { name: "xyz".to_string(), age: 18 };

    let mut v: Vec<&Employee> = Vec::new();
    v.push(&t);
    v.push(&t2);

    for it in &v {
        println!("i am a {}", *it);
    }
}

我想以多态方式调用特征对象向量引用的 2 个具体类型的显示。我收到以下编译错误:

<std macros>:2:21: 2:52 error: the trait `core::marker::Sized` is not implemented for the type `Employee` [E0277]
<std macros>:2 $ dst . write_fmt ( format_args ! ( $ ( $ arg ) * ) ) )
                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<std macros>:2:21: 2:52 note: in this expansion of format_args!

向量迭代应该调用具体类型的Display函数...

Answer 1

这终于成功了，谢谢:

use std::fmt;

struct TeamMember {
    name: String,
    age: u32,
}
struct Manager {
    name: String,
    age: u32,
}

impl fmt::Display for TeamMember {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "TeamMember!; name => {}, age => {}", self.name, self.age)
    }
}

impl fmt::Display for Manager {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "Manager!; name => {}, age => {}", self.name, self.age)
    }
}

trait Employee: fmt::Display {}
impl Employee for TeamMember {}
impl Employee for Manager {}

fn main() {
    let t = TeamMember {
        name: "abc".to_string(),
        age: 23,
    };
    let t2 = Manager {
        name: "xyz".to_string(),
        age: 18,
    };

    let mut v: Vec<&Employee> = Vec::new();
    v.push(&t);
    v.push(&t2);

    for it in &v {
        println!("i am a {}", *it);
    }
}