如何在 Rust 中对“选项"分配进行分组? [英] How to group 'Option' assignments in Rust?

问题描述

我有一个代码块，其中需要一次分配多个可选变量.任何值都是 None 的可能性很小，因此单独处理每个失败的案例并不是特别有用.

I have a block of code where multiple optional variables need to be assigned at once. There is very little chance any of the values will be None, so individually handing each failed case isn't especially useful.

目前我写的支票是这样的:

Currently I write the checks like this:

if let Some(a) = foo_a() {
    if let Some(b) = foo_b() {
        if let Some(c) = foo_c() {
            if let Some(d) = foo_d() {
                // code
            }
        }
    }
}

如果可以对作业进行分组会很方便.如果没有这个，添加一个新变量会使块缩进一级，从而产生嘈杂的差异并导致不必要的深度缩进:

It would be convenient if it was possible to group assignments. Without this, adding a new variable indents the block one level, making for noisy diffs and causes unnecessarily deep indentation:

if let Some(a) = foo_a() &&
   let Some(b) = foo_b() &&
   let Some(c) = foo_c() &&
   let Some(d) = foo_d()
{
    // code
}

有没有办法在一个 if 语句中分配多个 Option ?

Is there a way to assign multiple Options in one if statement?

一些值得注意的细节:

第一个失败的函数应该短路而不是调用其他函数.否则，它可以写成这样:

The first function that fails should short circuit and not call the others. Otherwise, it could be written like this:

if let (Some(a), Some(b), Some(c), Some(d)) = (foo_a(), foo_b(), foo_c(), foo_d()) {
    // Code
}

使用函数可以避免深度缩进，但我不希望这样做，因为您可能不希望正文处于不同的范围...

Deep indentation could be avoided using a function, but I would prefer not to do this since you may not want to have the body in a different scope...

fn my_function(a: Foo, b: Foo, c: Foo, d: Foo) {
    // code
}

if let Some(a) = foo_a() {
    if let Some(b) = foo_b() {
        if let Some(c) = foo_c() {
            if let Some(d) = foo_d() {
                my_function(a, b, c, d);
            }
        }
    }
}

推荐答案

正如 @SplittyDev 所说，你可以创建一个宏来获得你想要的功能.这是一个替代的基于宏的解决方案，它也保留了短路行为:

As @SplittyDev said, you can create a macro to get the functionality you want. Here is an alternate macro-based solution which also retains the short-circuiting behaviour:

macro_rules! iflet {
    ([$p:pat = $e:expr] $($rest:tt)*) => {
        if let $p = $e {
            iflet!($($rest)*);
        }
    };
    ($b:block) => {
        $b
    };
}


fn main() {
    iflet!([Some(a) = foo_a()] [Some(b) = foo_b()] [Some(c) = foo_c()] {
        println!("{} {} {}", a, b, c);
    });
}

游乐场

这篇关于如何在 Rust 中对“选项"分配进行分组?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！