在Rust中引用匹配值 [英] Referring to matched value in Rust

问题描述

假设我有以下代码:

fn non_zero_rand() -> i32 {
    let x = rand();
    match x {
        0 => 1,
        _ => x,
    }
}

是否有一种简便的方法将rand()放入比赛中，然后将其绑定到一个值.例如.像这样的东西:

Is there a concise way to put the rand() in the match, and then bind it to a value. E.g. something like this:

fn non_zero_rand() -> i32 {
    match let x = rand() {
        0 => 1,
        _ => x,
    }
}

或者:

fn non_zero_rand() -> i32 {
    match rand() {
        0 => 1,
        _x => _x,
    }
}

推荐答案

一个简单的变量将匹配所有值并引入新变量，例如:

A simple variable will match all values and introduce the new variable, e.g.:

match rand() {
    0 => 1,
    x => x * 2,
}

使用@模式创建和匹配变量的更通用的方法:

A more general way to create a variable and match it is using the @ pattern:

match rand() {
    0 => 1,
    x @ _ => x * 2,
}

在这种情况下，这不是必需的，但是在处理范围时会很有用:

In this case it is not necessary, but it can come useful when dealing with ranges:

match code {
    None => Empty,
    Some(ascii @ 0 ... 127) => Ascii(ascii as u8),
    Some(latin1 @ 160 ... 255) => Latin1(latin1 as u8),
    _ => Invalid
}

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