如何在 Vec 上将 trait 变成泛型<t> ?</t>

Question

我有一个工作特点：

trait PopOrErr {
    fn pop_or_err(&mut self) -> Result<i8, String>;
}

impl PopOrErr for Vec<i8> {
    fn pop_or_err(&mut self) -> Result<i8, String> {
        self.pop().ok_or_else(|| "stack empty".to_owned())
    }
}

我试过了：

trait PopOrErr<T> {
    fn pop_or_err(&mut self) -> Result<T, String>;
}

impl PopOrErr<T> for Vec<T> {
    fn pop_or_err(&mut self) -> Result<T, String> {
        self.pop().ok_or_else(|| "stack empty".to_owned())
    }
}

但它给了我：

error[E0412]: cannot find type `T` in this scope
  --> src/main.rs:29:15
   |
29 | impl PopOrErr<T> for Vec<T> {
   |     -         ^ not found in this scope
   |     |
   |     help: you might be missing a type parameter: `<T>`

error[E0412]: cannot find type `T` in this scope
  --> src/main.rs:29:26
   |
29 | impl PopOrErr<T> for Vec<T> {
   |     -                    ^ not found in this scope
   |     |
   |     help: you might be missing a type parameter: `<T>`

error[E0412]: cannot find type `T` in this scope
  --> src/main.rs:30:40
   |
29 | impl PopOrErr<T> for Vec<T> {
   |     - help: you might be missing a type parameter: `<T>`
30 |     fn pop_or_err(&mut self) -> Result<T, String> {
   |                                        ^ not found in this scope

如何在向量中包含的类型上使PopOrErr泛型？

Answer 1

“您可能缺少类型参数： <T> ”编译器试图提供帮助。 把<T>放在它说的地方，你对 go 很好。

trait PopOrErr<T> {
    fn pop_or_err(&mut self) -> Result<T, String>;
}

// Add it here: impl<T>
impl<T> PopOrErr<T> for Vec<T> {
    fn pop_or_err(&mut self) -> Result<T, String> {
        self.pop().ok_or("stack empty".to_string())
    }
}

你有一个与 ok_or_else 无关的错误，我用上面的ok_or替换了它。

如果您对为什么需要将泛型与impl和fn一起使用感到好奇，请查看此问题