Question

下面是我在 Rust 中比较 2 个 enum 变量的代码。

I uploaded the code into playground here.。

非常简单，我只想使用相等运算符 (==) 来比较两个枚举变量。提前致谢。

我的枚举：

use std::fmt::Display;

#[derive(Display)]
enum Fruits {
    Apple, 
    Orange,
}
// I try to use ToString but Rust cannot find derive macro `Display` in this scope
// ERROR: 
// doesn't satisfy `Fruits: ToString`
// doesn't satisfy `Fruits: std::fmt::Display`

// had to implement PartialEq for Fruits
impl PartialEq for Fruits {
    fn eq(&self, other: &Self) -> bool {
        self.to_string() == other.to_string()
        // here, I'm trying to use string conversion to compare both enum
        // it displays an error: 
        // method cannot be called on `&Fruits` due to unsatisfied trait bounds
    }
}

我的 main.rs：

fn main(){
    let a = Fruits::Apple;
    let b = Fruits::Orange;
    let c = Fruits::Apple;
    
    if a == c {
        println!("Correct! A equals with C !");
    }
    
    
     if a != b {
        println!("Correct! A is not equal with B !");
    }
    
}

Answer 1

如果要比较枚举变体，请不要构建然后比较字符串。

比较枚举变体（和大多数结构）的简单解决方案是派生 PartialEq：

#[derive(PartialEq)]
enum Fruits {
    Apple, 
    Orange,
}
fn main() {
    dbg!(Fruits::Apple == Fruits::Orange); // false
    dbg!(Fruits::Orange == Fruits::Orange); // true
}

Answer 2

如何导出 Debug 而不是 Display？无法派生显示。

#[derive(Debug)]
enum Fruits {
    Apple, 
    Orange,
}

impl PartialEq for Fruits {
    fn eq(&self, other: &Self) -> bool {
        format!("{:?}", self) == format!("{:?}", other)
    }
}

fn main(){
    let a = Fruits::Apple;
    let b = Fruits::Orange;
    let c = Fruits::Apple;
    
    if a == c {
        println!("Correct! A equals with C !");
    }
     if a != b {
        println!("Correct! A is not equal with B !");
    }
}

如何比较2个枚举变量？

2 个答案: