如何在尝试实施方法时修复“错误的类型参数数量”？

Question

我想实现一个方法：

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()); 
} 

我得到这个错误：

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

是什么原因造成这个问题？

Answer 1

你需要一个类型参数添加到IMPL：

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() 
    } 
}