如何在 Rust 中为值和引用实现惯用的运算符重载? [英] How to implement idiomatic operator overloading for values and references in Rust?

问题描述

在实现基本的固定大小向量类型(例如float2)时，我希望支持Add 和Sub 特性.稍后，我会想要支持Mul 和*Assign.

When implementing a primitive fixed-size vector type (float2 for example), I want to support the Add and Sub traits. Later, I will want to support Mul and *Assign.

查阅文档和其他示例，我想出了这个:

Looking up the documentation and other examples, I came up with this:

use std::ops::{Add, Sub};

#[derive(Copy, Clone)]
struct float2(f64, f64);

impl Add for float2 {
    type Output = float2;
    fn add(self, _rhs: float2) -> float2 {
        float2(self.0 + _rhs.0, self.1 + _rhs.1)
    }
}

impl Sub for float2 {
    type Output = float2;
    fn sub(self, _rhs: float2) -> float2 {
        float2(self.0 - _rhs.0, self.1 - _rhs.1)
    }
}

这适用于基本示例，但是我发现在实践中我经常以引用作为参数以及堆栈上的本地 float2 的引用结束.

This works for basic examples, however I found in practice I would often end up with references passed in as arguments as well as local float2's on the stack.

要混合这些，我需要:

• 取消引用变量(可以，但会使代码可读性稍差).
• 也声明运算符重载引用组合.

示例:

impl<'a, 'b> Add<&'b float2> for &'a float2 {
    type Output = float2;
    fn add(self, _rhs: &'b float2) -> float2 {
        float2(self.0 + _rhs.0, self.1 + _rhs.1)
    }
}
impl<'a> Add<float2> for &'a float2 {
    type Output = float2;
    fn add(self, _rhs: float2) -> float2 {
        float2(self.0 + _rhs.0, self.1 + _rhs.1)
    }
}
impl<'b> Add<&'b float2> for float2 {
    type Output = float2;
    fn add(self, _rhs: &'b float2) -> float2 {
        float2(self.0 + _rhs.0, self.1 + _rhs.1)
    }
}

/*... and again for Sub */

虽然这允许在不取消引用的情况下编写表达式.枚举每个组合变得非常乏味，尤其是在添加更多操作时类型(float3、float4...).

While this allows to write expressions without de-referencing. it becomes quite tedious to enumerate each combinations, especially when adding more operations & types (float3, float4...).

是否有一种普遍接受的方式来...

Is there a generally accepted way to...

• 为运算符重载自动强制类型?
• 使用宏或语言的其他一些特性来避免繁琐的重复?

或者希望开发人员:

• 根据需要显式访问变量作为引用.
• 根据需要显式取消引用变量.
• 编写大量重复的运算符重载函数.

注意，我目前是初学者，我已经检查了 Rust 中的一些非常高级的数学库，它们让我无法理解，而我可以使用它们 - 我想了解如何编写运算符重载我自己的类型.

推荐答案

Rust 的伟大之处在于它是开源的.这意味着您可以看到该语言的作者如何解决问题.最接近的类似物是 原始整数类型:

The great thing about Rust is that it's open source. This means you can see how the authors of the language have solved a problem. The closest analogue is primitive integer types:

macro_rules! add_impl {
    ($($t:ty)*) => ($(
        #[stable(feature = "rust1", since = "1.0.0")]
        impl Add for $t {
            type Output = $t;

            #[inline]
            fn add(self, other: $t) -> $t { self + other }
        }

        forward_ref_binop! { impl Add, add for $t, $t }
    )*)
}

forward_ref_binop 定义为:

macro_rules! forward_ref_binop {
    (impl $imp:ident, $method:ident for $t:ty, $u:ty) => {
        #[stable(feature = "rust1", since = "1.0.0")]
        impl<'a> $imp<$u> for &'a $t {
            type Output = <$t as $imp<$u>>::Output;

            #[inline]
            fn $method(self, other: $u) -> <$t as $imp<$u>>::Output {
                $imp::$method(*self, other)
            }
        }

        #[stable(feature = "rust1", since = "1.0.0")]
        impl<'a> $imp<&'a $u> for $t {
            type Output = <$t as $imp<$u>>::Output;

            #[inline]
            fn $method(self, other: &'a $u) -> <$t as $imp<$u>>::Output {
                $imp::$method(self, *other)
            }
        }

        #[stable(feature = "rust1", since = "1.0.0")]
        impl<'a, 'b> $imp<&'a $u> for &'b $t {
            type Output = <$t as $imp<$u>>::Output;

            #[inline]
            fn $method(self, other: &'a $u) -> <$t as $imp<$u>>::Output {
                $imp::$method(*self, *other)
            }
        }
    }
}

为引用编写特性的包装器实现当然是有效的，这些引用只是取消引用并调用面向值的版本.​​

It's certainly valid to write wrapper implementations of the traits for references that simply dereference and call the value-oriented version.

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