Rust 中的 Subclassing特征

我遇到的情况是，我的几个 struct 应该实现多个特性，但它们都至少实现了一个共同的特性.当我得到这些 struct 的混合包时，我想把它们都视为共同特征:将它们作为键入该特征的方法参数传递，存储在为该特征键入的集合中，等等.

我还不知道怎么做.下面是一些代码，我try 按照这里建议的方式执行，但未能编译:

trait ThingWithKeys {
    fn use_keys (&self) -> String;
}

//////

trait CorrectionsOfficer {
    fn hitch_up_pants (&self) -> String;
}

trait CorrectionsOfficerWithKeys: ThingWithKeys + CorrectionsOfficer {}

struct CorrectionsOfficerReal {}

impl ThingWithKeys for CorrectionsOfficerReal {
    fn use_keys (&self) -> String {
        String::from ("Clank, clank")
    }
}

impl CorrectionsOfficer for CorrectionsOfficerReal {
    fn hitch_up_pants (&self) -> String {
        String::from ("Grunt")
    }
}

impl <T: ThingWithKeys + CorrectionsOfficer> CorrectionsOfficerWithKeys for T {}

//////

trait Piano {
    fn close_lid (&self) -> String;
}

trait PianoWithKeys: Piano + ThingWithKeys {}

struct PianoReal {}

impl ThingWithKeys for PianoReal {
    fn use_keys (&self) -> String {
        String::from ("Tinkle, tinkle")
    }
}

impl Piano for PianoReal {
    fn close_lid (&self) -> String {
        String::from ("Bang!")
    }
}

impl <T: ThingWithKeys + Piano> PianoWithKeys for T {}

//////

trait Florida {
    fn hurricane (&self) -> String;
}

trait FloridaWithKeys: ThingWithKeys + Florida {}

struct FloridaReal {}

impl ThingWithKeys for FloridaReal {
    fn use_keys (&self) -> String {
        String::from ("Another margarita, please")
    }
}

impl Florida for FloridaReal {
    fn hurricane (&self) -> String {
        String::from ("Ho-hum...")
    }
}

impl <T: ThingWithKeys + Florida> FloridaWithKeys for T {}

//////

fn main() {
    let corrections_officer_ref: &CorrectionsOfficerWithKeys = &CorrectionsOfficerReal {};
    let piano_ref: &PianoWithKeys = &PianoReal {};
    let florida_ref: &FloridaWithKeys = &FloridaReal {};

    use_keys (corrections_officer_ref);
    use_keys (piano_ref);
    use_keys (florida_ref);
}

fn use_keys (thing_with_keys: &ThingWithKeys) {
    println! ("{}", thing_with_keys.use_keys ());
}

以下是编译错误:

Compiling playground v0.0.1 (file:///playground)
error[E0308]: mismatched types
  --> src/main.rs:80:19
   |
80 |         use_keys (corrections_officer_ref);
   |                   ^^^^^^^^^^^^^^^^^^^^^^^ expected trait `ThingWithKeys`, found trait `CorrectionsOfficerWithKeys`
   |
   = note: expected type `&ThingWithKeys`
              found type `&CorrectionsOfficerWithKeys`

error[E0308]: mismatched types
  --> src/main.rs:81:19
   |
81 |         use_keys (piano_ref);
   |                   ^^^^^^^^^ expected trait `ThingWithKeys`, found trait `PianoWithKeys`
   |
   = note: expected type `&ThingWithKeys`
              found type `&PianoWithKeys`

error[E0308]: mismatched types
  --> src/main.rs:82:19
   |
82 |         use_keys (florida_ref);
   |                   ^^^^^^^^^^^ expected trait `ThingWithKeys`, found trait `FloridaWithKeys`
   |
   = note: expected type `&ThingWithKeys`
              found type `&FloridaWithKeys`

error: aborting due to 3 previous errors

本质上，它仍然无法在XxxWithKeys实现中找到ThingWithKeys实现.