这可能是一个我还不知道的功能。我有这个编译器消息：

$ cargo build --lib
  Compiling secondimpl v0.1.0 (/home/nsdd/garage/sames/rustex/secondimpl)
 warning: field `somebool` is never read
 --> src/lib.rs:6:5
  |
5 | pub struct ExampleStruct {
  |            ------------- field in this struct
6 |     somebool: bool,
  |     ^^^^^^^^
  |
  = note: `#[warn(dead_code)]` on by default

 warning: associated function `playhere` is never used
  --> src/lib.rs:31:8
   |
31 |     fn playhere(&self) -> usize {
   |        ^^^^^^^^

warning: `secondimpl` (lib) generated 2 warnings
    Finished dev [unoptimized + debuginfo] target(s) in 0.16s

字符串
这是我的示例代码：

pub trait ExampleTrait {
    fn new(mynum: usize) -> Self;
}

pub struct ExampleStruct {
    somebool: bool,
    somenum: usize,
}

impl Default for ExampleStruct {
    fn default() -> Self {
        ExampleStruct {
            somebool: true,
            somenum: 999,
        }
    }
}

impl ExampleTrait for ExampleStruct {

    fn new(mynum: usize) -> Self {
        let mut buffer: ExampleStruct = Default::default();
        buffer.somenum = mynum;
        return buffer;
    }

}

impl ExampleStruct {

    fn playhere(&self) -> usize {
        if self.somebool {
            return self.somenum;
        }
        return 0;
    }

}

型
因为我只在第二个impl中使用了self.somenum，所以编译器似乎不喜欢它。大概我可以做一些声明或语法更改来阻止这个警告，因为这显然是一个没有考虑第二个impl的问题。该字段不会出现在其他trait中，所以我不能把它放在trait中。