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Rick de Water's questions

Martin Hope
Rick de Water
Asked: 2023-08-17 20:58:04 +0800 CST
  • 9

在下面的简化示例中，编译器抱怨语句的一个分支match返回bool，而另一个分支返回()。

use std::collections::{HashMap, HashSet};

fn main() {
    let available = HashMap::from_iter([(2, "b"), (3, "c"), (4, "d")]);
    let mut set = HashSet::new();
    
    for i in [1, 2, 3, 4, 5] {
        match available.get(&i) {
            Some(s) => set.insert(*s),
            None => ()
        }
    }
}

但这会导致错误：

error[E0308]: `match` arms have incompatible types
  --> src/main.rs:10:21
   |
8  | /         match available.get(&i) {
9  | |             Some(s) => set.insert(*s),
   | |                        -------------- this is found to be of type `bool`
10 | |             None => ()
   | |                     ^^ expected `bool`, found `()`
11 | |         }
   | |_________- `match` arms have incompatible types

如何通知编译器 match 语句应该 return ()，并且bool返回的 frominsert应该被忽略？

rust