当模式匹配类似结构的枚举变体与字段时,为什么会出现错误？

Question

我无法摆脱这段代码的错误:

#[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(_) => {},
        };
    }
}

decrypt函数末尾的模式匹配会产生错误:

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 --explain E0532帮助的输出,我做了.

他们展示了错误代码的示例:

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具有不匹配的字段.它应该是State::Failed(ref msg).

在我的情况下,我匹配我的枚举字段,因为我正在做 OperationMode::CBC(_).为什么会发生错误？

Answer 1

枚举变体有三种可能的语法:

• 单元

  enum A { One }
  

• 元组

  enum B { Two(u8, bool) }
  

• 结构

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

模式匹配时必须使用相同的语法作为变体定义的语法.

在这种情况下,你需要花括号和..全能:

OperationMode::CBC { .. } => {}