rust - "consider removing this semicolon"错误

Question

同时关注 rustbyexample.com教程中，我输入了以下代码:

impl fmt::Display for Structure {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let x = format!("{}", "something");
        write!(f, "OMG! {}", self.0);
    }   
}   

并从编译器中得到以下错误:

error[E0308]: mismatched types
 --> src/main.rs:5:58
  |
5 |       fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
  |  __________________________________________________________^
6 | |         let x = format!("{}", "something");
7 | |         write!(f, "OMG! {}", self.0);
8 | |     }   
  | |_____^ expected enum `std::result::Result`, found ()
  |
  = note: expected type `std::result::Result<(), std::fmt::Error>`
             found type `()`
help: consider removing this semicolon:
 --> src/main.rs:7:37
  |
7 |         write!(f, "OMG! {}", self.0);
  |                                     ^

为什么分号在这里相关(或不相关)？

Answer 1

Rust 函数的返回值是最后一个不跟分号的表达式。使用分号，您的方法不会返回任何内容。没有最后一个分号，它返回 write!(f, "OMG! {}", self.0) 的值。

您可以阅读更多相关信息 in The Rust Programming Language chapter about functions ;查找以“如何返回一个值？”开头的部分。