如何模式匹配Vec< T>在没有嵌套匹配的枚举区域内？ [英] How can I pattern-match a Vec<T> inside an enum field without nesting matches?

问题描述

模式匹配 Vec 可以通过使用& v [..] 或 v.as_slice（）。

Pattern-matching a Vec<T> can be done by using either &v[..] or v.as_slice().

let x = vec![1, 2, 3];
match &x[..] {
    [] => println!("empty"),
    [_] => println!("one"),
    [..] => println!("many"),
}

如果我有一个字段的枚举包含我想要匹配的 Vec ，我需要在外部匹配手段中创建一个嵌套的匹配：

If I have an enum with a field that contains the Vec I want to match on, I need to create a nested match inside the outer match arm:

enum Test {
    Many(Vec<u8>),
    Text(String),
}

fn main() {
    let x = Test::Many(vec![1, 2, 3]);
    match x {
        Test::Text(s) => println!("{}", s),
        Test::Many(v) => match &v[..] {
            [] => println!("empty"),
            [_] => println!("one"),
            [..] => println!("many"),
        }
    }
}

我想要做的是直接匹配 Vec ，如下例所示：

What I would like to be able to do, is to match directly on the Vec as in the following example:

match x {
    Test::Text(s) => println!("{}", s),
    Test::Many([]) => println!("empty"),
    Test::Many([_]) => println!("one"),
    Test::Many([..]) => println!("many"),
}

我猜，一个href =https://github.com/rust-lang/rust/pull/12244/files#diff-ca04b724f2df29e92436ba8d2e09e18bL12 =nofollow>唯一的矢量被删除？或者我使用可以解决这个问题的 ref 缺少一些魔法。

I am guessing it was possible before unique vectors got removed? Or am I missing some magic using ref that can solve this?

推荐答案

Deref 模式，这将允许通过实现 Deref 的任何类型的模式匹配或 DerefMut ，例如可以在框< T> 中的 T 上匹配，或者在 [T ] insidea Vec< T> 。

It's not possible to do this directly, unfortunately. However, there is desire to possibly add "Deref patterns", which would allow pattern matching through any types which implement Deref or DerefMut, e.g. one could match on the T inside a Box<T>, or on the [T] "inside" a Vec<T>.

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