Question

在下面的例子中，我想在数组中添加2个元素，在2个元素上有一个简单的加法，声明为内联，并从数组中访问。

use std::ops::Add;
use std::fmt;

struct Vector(f64, f64);

impl Add for Vector {
    type Output = Vector;

    fn add(self, _rhs: Vector) -> Vector {
        Vector(self.0 + _rhs.0,
               self.1 + _rhs.1)
    }
}

impl fmt::Display for Vector {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "({}, {})", self.0, self.1)
    }
}

fn main() {
    let points: [Vector; 2] = [
        Vector(1.0, 1.0),
        Vector(5.0, 5.0),
    ];

    /* Adding from an array fails somehow: */

    // let v: Vector = Vector(1.0, 1.0) + Vector(5.0, 5.0);    // This works!

    let v: Vector = points[0] + points[1];                     // This fails!

    println!("Vector is {}\n", v);
}

出于某种原因，let v: Vector = points[0] + points[1];会出错：

main.rs:37:21: 37:30 error: cannot move out of type `[Vector; 2]`, a non-copy fixed-size array [E0508]
main.rs:37     let v: Vector = points[0] + points[1];                     // This fails!

如何避免此错误并对数组元素执行操作符重载操作？

Answer 1

事实证明我需要添加对&Vector类型的支持，然后将数组元素作为引用访问。

这是一个有效的例子：

use std::ops::Add;
use std::fmt;

struct Vector(f64, f64);

impl Add for Vector {
    type Output = Vector;

    fn add(self, _rhs: Vector) -> Vector {
        Vector(self.0 + _rhs.0,
               self.1 + _rhs.1)
    }
}

impl<'a, 'b> Add<&'b Vector> for &'a Vector {
    type Output = Vector;

    fn add(self, _rhs: &'b Vector) -> Vector {
        Vector(self.0 + _rhs.0,
               self.1 + _rhs.1)
    }
}


impl fmt::Display for Vector {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "({}, {})", self.0, self.1)
    }
}

fn main() {
    let points: [Vector; 2] = [
        Vector(1.0, 1.0),
        Vector(5.0, 5.0),
    ];

    let v: Vector = &points[0] + &points[1];

    println!("Vector is {}\n", v);
}

Answer 2

您可以使Vector元组结构从Copy和Clone特征派生。因此编译器可以从数组中复制元素。

use std::ops::Add;
use std::fmt;

#[derive(Copy, Clone)]
struct Vector(f64, f64);

impl Add for Vector {
    type Output = Vector;

    fn add(self, _rhs: Vector) -> Vector {
        Vector(self.0 + _rhs.0,
               self.1 + _rhs.1)
    }
}

impl fmt::Display for Vector {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "({}, {})", self.0, self.1)
    }
}

fn main() {
    let points: [Vector; 2] = [
        Vector(1.0, 1.0),
        Vector(5.0, 5.0),
    ];

    let v: Vector = points[0] + points[1];

    println!("Vector is {}\n", v);
}

对数组元素执行操作时出错：“无法移出类型”

2 个答案: