通用特征中的不匹配类型

Question

我是Rust的新手，来自C ++背景，我在通用特性中实现默认行为时遇到了一些麻烦。通用Rectangle特征的以下样本特征（适用于i32和f32）：

trait Rectangle<T: PartialOrd> {
    fn left(&self)   -> f32;
    fn top(&self)    -> f32;
    fn right(&self)  -> f32;
    fn bottom(&self) -> f32;

    fn x(&self)      -> f32 { self.left() }
    fn y(&self)      -> f32 { self.top()  }
    fn width(&self)  -> f32 { self.right()  - self.left() }
    fn height(&self) -> f32 { self.bottom() - self.top()  }

    fn is_empty(&self) -> bool {
        self.left() >= self.right() || self.top() >= self.bottom()
    }

    fn set_ltrb(&mut self, l: T, t: T, r: T, b: T);
    fn set_xywh(&mut self, x: T, y: T, w: T, h: T);
    fn set_wh(&mut self, w: T, h: T);

    fn offset(&mut self, dx: T, dy: T);

    fn intersects(&self, other: &Rectangle<T>) -> bool {
        let l =  self.left().max(other.left());
        let t =  self.top().max(other.top());
        let r =  self.right().max(other.right());
        let b =  self.bottom().max(other.bottom());

        l < r && t < b
    }
    fn intersect(&mut self, other: &Rectangle<T>) -> bool {
        let l =  self.left().max(other.left());
        let t =  self.top().max(other.top());
        let r =  self.right().max(other.right());
        let b =  self.bottom().max(other.bottom());

        if l < r && t < b {
            self.set_ltrb(l,t,r,b); // This is the offending line
            true
        } else {
            false
        }
    }
}

pub struct Rect<T> {
    pub left:   T,
    pub top:    T,
    pub right:  T,
    pub bottom: T,
}

pub type IRect = Rect<i32>;
pub type FRect = Rect<f32>;

导致出现此错误消息：

   Compiling dinky v0.1.0 (file:///home/menozzi/Desktop/projects/dinky)
src/rect.rs:37:27: 37:28 error: mismatched types:
 expected `T`,
    found `f32`
(expected type parameter,
    found f32) [E0308]
src/rect.rs:37             self.set_ltrb(l,t,r,b);
                                         ^
src/rect.rs:37:27: 37:28 help: run `rustc --explain E0308` to see a detailed explanation
src/rect.rs:37:29: 37:30 error: mismatched types:
 expected `T`,
    found `f32`
(expected type parameter,
    found f32) [E0308]
src/rect.rs:37             self.set_ltrb(l,t,r,b);
                                           ^
src/rect.rs:37:29: 37:30 help: run `rustc --explain E0308` to see a detailed explanation
src/rect.rs:37:31: 37:32 error: mismatched types:
 expected `T`,
    found `f32`
(expected type parameter,
    found f32) [E0308]
src/rect.rs:37             self.set_ltrb(l,t,r,b);
                                             ^
src/rect.rs:37:31: 37:32 help: run `rustc --explain E0308` to see a detailed explanation
src/rect.rs:37:33: 37:34 error: mismatched types:
 expected `T`,
    found `f32`
(expected type parameter,
    found f32) [E0308]
src/rect.rs:37             self.set_ltrb(l,t,r,b);
                                               ^
src/rect.rs:37:33: 37:34 help: run `rustc --explain E0308` to see a detailed explanation
error: aborting due to 4 previous errors
Could not compile `dinky`.

To learn more, run the command again with --verbose.

知道为什么这种类型不匹配？