while let

与 if let 类似，while let 可以使笨拙的 match 序列更易于接受。考虑以下递增 i 的序列

#![allow(unused)]
fn main() {
// Make `optional` of type `Option<i32>`
let mut optional = Some(0);

// Repeatedly try this test.
loop {
    match optional {
        // If `optional` destructures, evaluate the block.
        Some(i) => {
            if i > 9 {
                println!("Greater than 9, quit!");
                optional = None;
            } else {
                println!("`i` is `{:?}`. Try again.", i);
                optional = Some(i + 1);
            }
            // ^ Requires 3 indentations!
        },
        // Quit the loop when the destructure fails:
        _ => { break; }
        // ^ Why should this be required? There must be a better way!
    }
}
}

使用 while let 使这个序列更简洁

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另请参阅

enum，Option，以及 RFC