如何在尝试实现方法时修复“错误数量的类型参数”？

Question

我正在尝试实现一个方法：

struct Point<T> {
    x: T,
    y: T,
}

struct Line<T> {
    start: Point<T>,
    end: Point<T>,
}

impl Line {
    fn length(&self) -> f64 {
        let dx: f64 = self.start.x - self.end.x;
        let dy: f64 = self.start.y - self.end.y;
        (dx * dx + dy * dy).sqrt()
    }
}

fn main() {
    let point_start: Point<f64> = Point { x: 1.4, y: 1.24 };
    let point_end: Point<f64> = Point { x: 20.4, y: 30.64 };

    let line_a: Line<f64> = Line {
        start: point_start,
        end: point_end,
    };
    println!("length of line_a = {}", line_a.length());
}

我收到此错误：

error[E0243]: wrong number of type arguments: expected 1, found 0
  --> src/main.rs:11:6
   |
11 | impl Line {
   |      ^^^^ expected 1 type argument

是什么导致了这个问题？

Answer 1

你需要给impl添加一个类型参数：

impl Line<f64> {
    fn length(&self) -> f64 {
        let dx: f64 = self.start.x - self.end.x;
        let dy: f64 = self.start.y - self.end.y;
        (dx * dx + dy * dy).sqrt()
    }
}