Rust if let Optionals 和比较条件

Question

我有很多这样的代码，我想用 "if let" 绑定(bind)来替换我的情况以清晰明了

// contrived
fn maybe() -> Option<i32> { Some(1)}
let maybe_num_A = maybe();
let maybe_num_B = maybe();
...
match (maybe_num_A, maybe_num_B) {
  (Some(a) , Some(b)) if a > b => {
      .... 
  }
  _ => {} // don't care many times about the other matches that doesn't hold. how to get rid of this?
}

不确定用比较绑定(bind) let 的语法:

if let (Some(a),Some(b) = (maybe_num_A, maybe_num_B) ???&&??? a > b {
   ... 
}

Answer 1

如果您只是比较A 和B 并且不一定需要绑定(bind)它们，您可以使用.zip Rust 1.46 中的方法并申请 map_or在上面，例如:

let a: Option<i32> = Some(42);
let b: Option<i32> = Some(-42);

if a.zip(b).map_or(false, |(a, b)| a > b) {
   // 42 is greater than -42
}

如果两个值中的任何一个为None，它将默认为false。