rust - 深度嵌套枚举的清洁匹配臂

Question

我有以下带有匹配表达式的函数:

fn handle_event<'e>(&mut self, event: Event<'e>) -> Event<'e> {
    match (&event, &self.current_lang) {
        (Event::Start(Tag::CodeBlock(CodeBlockKind::Fenced(lang))), _) => {
            self.start_fenced_code_block(&lang)
        }
        (Event::End(Tag::CodeBlock(CodeBlockKind::Fenced(_))), _) => {
            self.end_fenced_code_block()
        }
        (Event::Text(text), Some(lang)) => self.code_html(&text, &lang),
        _ => event,
    }
}

但是，由于嵌套很深的枚举，前两条 ARM 感觉像是失控了。所以我做了一些宏:

macro_rules! fenced_code_block_start {
    ($lang:pat_param) => {
        Event::Start(Tag::CodeBlock(CodeBlockKind::Fenced($lang)))
    };
}
macro_rules! fenced_code_block_end {
    () => {
        Event::End(Tag::CodeBlock(CodeBlockKind::Fenced(_)))
    };
}

现在我有了，恕我直言，更清洁:

match (&event, &self.current_lang) {
    (fenced_code_block_start!(lang), _) => self.start_fenced_code_block(&lang),
    (fenced_code_block_end!(), _) => self.end_fenced_code_block(),
    (Event::Text(text), Some(lang)) => self.code_html(&text, &lang),
    _ => event,
}

不过，我想知道是否有更好的方法来做到这一点。下降到宏总是让我停下来。我可以在这里使用 Rust 的其他一些功能，而不是这么重的锤子吗？

Answer 1

如果不丢失清晰度，您可以直接导入和使用枚举变体:

fn handle_event<'e>(&mut self, event: Event<'e>) -> Event<'e> {
    use Event::*;
    use Tag::*;
    use CodeBlockKind::*;
    
    match (&event, &self.current_lang) {
        (Start(CodeBlock(Fenced(lang))), _) => self.start_fenced_code_block(&lang),
        (End(CodeBlock(Fenced(_))), _) => self.end_fenced_code_block(),
        (Text(text), Some(lang)) => self.code_html(&text, &lang),
        _ => event,
    }
}