在将类似结构的枚举变量与字段进行模式匹配时，为什么会出现错误？ [英] Why do I get an error when pattern matching a struct-like enum variant with fields?

问题描述

我无法清除此代码上的错误：

I can't get rid of an error on this code:

#[derive(PartialEq, Copy, Clone)]
pub enum OperationMode {
    ECB,
    CBC { iv: [u8; 16] },
}

pub struct AES {
    key: Vec<u8>,
    nr: u8,
    mode: OperationMode,
}

impl AES {
    pub fn decrypt(&mut self, input: &Vec<u8>) {
        match self.mode {
            OperationMode::ECB => {},
            OperationMode::CBC(_) => {},
        };
    }
}

<$ c末尾的模式匹配$ c>解密函数给出错误：

error[E0532]: expected tuple struct/variant, found struct variant `OperationMode::CBC`
  --> src/main.rs:17:13
   |
17 |             OperationMode::CBC(_) => {},
   |             ^^^^^^^^^^^^^^^^^^ did you mean `OperationMode::CBC { /* fields */ }`?

它告诉我看看 rustc --exploin E0532 <的输出

It tells me to look at the output of rustc --explain E0532 for help, which I did.

他们显示了以下示例错误代码：

They show this example of wrong code:

enum State {
    Succeeded,
    Failed(String),
}

fn print_on_failure(state: &State) {
    match *state {
        // error: expected unit struct/variant or constant, found tuple
        //        variant `State::Failed`
        State::Failed => println!("Failed"),
        _ => ()
    }
}

在此示例中，发生错误是因为 State :: Failed 的字段不匹配。应该是 State :: Failed（ref msg）。

In this example, the error occurs because State::Failed has a field which isn't matched. It should be State::Failed(ref msg).

在我的情况下，我匹配的是我的枚举，因为我正在执行 OperationMode :: CBC（_）。为什么会发生错误？

In my case I'm matching the field of my enum because I'm doing OperationMode::CBC(_). Why does the error happen?

推荐答案

枚举变量具有三种可能的语法：

Enum variants have three possible syntaxes:

• 单位

• unit

enum A { One }

元组

tuple

enum B { Two(u8, bool) }

struct

struct

enum C { Three { a: f64, b: String } }

模式匹配时，必须使用与变体定义的语法相同的语法：

You have to use the same syntax when pattern matching as the syntax the variant was defined as:

• 单位

• unit

match something {
    A::One => { /* Do something */ }
}

元组

tuple

match something {
    B::Two(x, y) => { /* Do something */ }
}

结构

struct

match something {
    C::Three { a: another_name, b } => { /* Do something */ }
}

除此之外，您可以使用各种允许忽略值的模式，例如 _ 或。. 。在这种情况下，您需要花括号和 .. 包罗万象：

Beyond that, you can use various patterns that allow ignoring a value, such as _ or ... In this case, you need curly braces and the .. catch-all:

OperationMode::CBC { .. } => { /* Do something */ }

另请参见：

• 使用 Rust编程语言


• 附录B： Rust编程语言
$ b中的运算符和符号$ b
• 如何在Rust中匹配结构字段？

• Ignoring Values in a Pattern in The Rust Programming Language
• Appendix B: Operators and Symbols in The Rust Programming Language
• How to match struct fields in Rust?

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