有没有办法匹配两个枚举变体并将匹配的变体绑定到变量? [英] Is there a way to match two enum variants and also bind the matched variant to a variable?

问题描述

我有这个枚举:

enum ImageType {
    Png,
    Jpeg,
    Tiff,
}

有没有办法匹配前两个之一，并将匹配的值绑定到一个变量?例如:

Is there any way to match one of the first two, and also bind the matched value to a variable? For example:

match get_image_type() {
    Some(h: ImageType::Png) | Some(h: ImageType::Jpeg) => {
        // Lots of shared code
        // that does something with `h`
    },
    Some(ImageType::Tiff) => { ... },
    None => { ... },
}

那个语法不起作用，但有什么可以吗?

That syntax doesn't work, but is there any that does?

推荐答案

您似乎在问如何绑定第一个案例中的值.如果是这样，你可以使用这个:

It looks like you are asking how to bind the value inside the first case. If so, you can use this:

match get_image_type() {
    // use @ to bind a name to the value
    Some(h @ ImageType::Png) | Some(h @ ImageType::Jpeg) => {
        // Lots of shared code that does something with `h`
    },
    Some(ImageType::Tiff) => { ... },
    None => { ... }
}

如果您还想在 match 语句之外获取绑定值，可以使用以下内容:

If you want to also get the bound value outside of the match statement, you can use the following:

let matched = match get_image_type() {
    Some(h @ ImageType::Png) | Some(h @ ImageType::Jpeg) => {
        // Lots of shared code that does something with `h`
        Some(h)
    },
    Some(h @ ImageType::Tiff) => {
        // ...
        Some(h)
    },
    None => {
        // ...
        None
    },
};

不过，在这种情况下，最好先简单地let h = get_image_type()，然后match h(感谢BHustus).

In that case, though, it might be better to simply let h = get_image_type() first, and then match h (thanks to BHustus).

注意使用 h @ 语法将变量名称 h 绑定到匹配的值(来源).

Note the use of the h @ <value> syntax to bind the variable name h to the matched value (source).

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