if let

在某些使用场景中，当匹配枚举时，match 会显得笨拙。例如：

#![allow(unused)]
fn main() {
// Make `optional` of type `Option<i32>`
let optional = Some(7);

match optional {
    Some(i) => println!("This is a really long string and `{:?}`", i),
    _ => {},
    // ^ Required because `match` is exhaustive. Doesn't it seem
    // like wasted space?
};

}

对于这种情况，if let 更简洁，并且允许指定各种失败时的处理选项。

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同样，if let 可以用来匹配任何枚举值。

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另一个好处是，if let 允许我们匹配未参数化的枚举变体。即使在枚举没有实现或派生 PartialEq 的情况下也是如此。在这样的情况下，if Foo::Bar == a 会编译失败，因为枚举的实例不能被比较，但是 if let 仍然可以工作。

你想接受一个挑战吗？修改下面的示例以使用 if let

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另请参阅

enum，Option，以及 RFC