知识点拾遗——Option 将其中的引用转换为值

fn main() {                                                                                        
      let x = 123u8;         
      let y: Option<&u8> = Some(&x);  
      let z: Option<u8> = y.copied(); 
    
      if let Some(xx) = z {
          println!("xx == {}", xx);
      }
      println!("Hello, world!");
 }