有没有办法让我隐式地绑定let/match操作的成员?

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英文:

Is there a way for me to implicitly bind the members of a let/match operation?

问题

在下面的代码中,ThreeD 是一个枚举类型,可以是 Point 或 Vector。函数 cross 的目的是计算两个 Vector 的叉积,并在其中任何一个参数是 Point 时引发错误。

为了计算结果,我需要左操作数(lhs)和右操作数(rhs)的 x、y 和 z 分量。然而,目前的代码中,第二个模式匹配会隐藏第一个模式匹配中的 x、y 和 z 成员。

一种选择是在第一个 let 语句之后显式地将 x、y 和 z 成员分配给临时变量,但这种方法感觉非常笨拙。

pub fn cross(lhs: ThreeD, rhs: ThreeD) -> ThreeD {
    if let Vector { x, y, z } = lhs {
        let lhs_x = x;    // 我不喜欢这种方法!
        let lhs_y = y;    //
        let lhs_z = z;    //

        if let Vector { x, y, z } = rhs {
            // 这里进行虚拟计算 - 我知道这是错误的 ;-)
            Vector { x: lhs_x * x, y: lhs_y * y, z: lhs_z * z }
        } else {
            panic!("无法计算点与点的叉积")
        }
    } else {
        panic!("无法计算点与点的叉积")
    }
}

如果你有任何其他问题,请随时提出。

英文:

E.g. in the code below, ThreeD is an enum which can either be a Point or a Vector. The function cross is intended to calculate the cross product of two Vectors, and panic if either argument is a Point.

In order to calculate the result I need the x, y and z components of both the lhs and the rhs. As it stands however the second match will obscure the x,y and z members from the first match.

One option is to explicitly assign the x, y, and z members to temporary variables, immediately after the first let statement, but this feels horribly klunky.

pub fn cross(lhs: ThreeD, rhs: ThreeD) -> ThreeD {
    if let Vector { x, y, z } = lhs {
        let lhs_x = x;    // I DON'T LIKE THIS APPROACH!
        let lhs_y = y;    //
        let lhs_z = z;    //

        if let Vector { x, y, z } = rhs {
            // dummy calc here - I know this is wrong ;-)
            Vector { x: lhs_x * x, y: lhs_y * y, z: lhs_z * z }
        } else {
            panic!("Cannot calculate cross product with a point")
        }
    } else {
        panic!("Cannot calculate cross product against a point")
    }
}

答案1

得分: 3

你可以使用以下语法在模式内将其绑定到不同的名称:

if let Vector { x: lhs_x, y: lhs_y, z: lhs_z } = lhs {
英文:

You can bind to a different name within the pattern using this syntax:

if let Vector { x: lhs_x, y: lhs_y, z: lhs_z } = lhs {

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  • 本文由 发表于 2023年5月29日 01:08:48
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