【Rust】if-let

环境

• Rust 1.56.1
• VSCode 1.61.2

概念

参考：https://doc.rust-lang.org/stable/rust-by-example/flow_control/if_let.html

示例

match 和 if-let 的比较

fn main() {
    let optional = Some(7);

    match optional {
        Some(i) => {
            println!("This is a really long string and `{:?}`", i);
        }
        _ => {}
    };

    if let Some(i) = optional {
        println!("This is a really long string and `{:?}`", i);
    };
}

不满足处理

fn main() {
    let letter: Option<i32> = None;
    if let Some(i) = letter {
        println!("Matched {:?}!", i);
    } else {
        println!("Didn't match a number. Let's go with a letter!");
    }
}

其它条件

fn main() {
    let emoticon: Option<i32> = None;
    let i_like_letters = false;

    if let Some(i) = emoticon {
        println!("Matched {:?}!", i);
    } else if i_like_letters {
        println!("Didn't match a number. Let's go with a letter!");
    } else {
        println!("I don't like letters. Let's go with an emoticon :)!");
    }
}

处理枚举值

enum Foo {
    Bar,
    Baz,
    Qux(u32),
}

fn main() {
    let a = Foo::Bar;
    let c = Foo::Qux(100);

    if let Foo::Bar = a {
        println!("a is foobar");
    }
    if let Foo::Qux(value) = c {
        println!("c is {}", value);
    }

    // 匹配绑定
    if let Foo::Qux(value @ 100) = c {
        println!("c is one hundred");
    }
}

总结

了解了 Rust 中 if-let 语法，有时候比使用 match 方便。

附录