特征名称后面的特征是什么意思？

Question

I came across this trait definition while reading about Rust:

trait Enchanter: std::fmt::Debug {
    ...
}

From this I understand that the name of the trait is Enchanter , but I do not understand what the std::Format:Debug part implies since it is also a trait (I think).

Answer 1

This is declaring a supertrait . It is equivalent to:

trait Enchanter
where
    Self: std::fmt::Debug,
{
}

In short, it requires any type that wants to implement Enchanter to also implementstd::fmt::Debug . Otherwise, an error will be raised :

error[E0277]: `S` doesn't implement `Debug`
 --> src/lib.rs:4:6
  |
4 | impl Enchanter for S {}
  |      ^^^^^^^^^ `S` cannot be formatted using `{:?}`
  |
  = help: the trait `Debug` is not implemented for `S`
  = note: add `#[derive(Debug)]` to `S` or manually `impl Debug for S`
note: required by a bound in `Enchanter`
 --> src/lib.rs:1:18
  |
1 | trait Enchanter: std::fmt::Debug {}
  |                  ^^^^^^^^^^^^^^^ required by this bound in `Enchanter`