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//对任何实现特定trait类型有条件的实现trait
trait GetName {
    fn get_name(&self) -> &String;
  }
trait PrintName {
    fn print_name(&self);
  }
//对泛型T实现了PrintName特征，前提是T实现了GetName
//有点类似继承
impl<T:GetName> PrintName for T {
      fn print_name(&self) {
          println!("name = {}",self.get_name());
        }
  }

struct Student {
    name: String,
  }
impl GetName for Student {
    fn get_name(&self) -> &String {
        &(self.name)
      }
  }

fn main() {
    let s = Student {
        name: String::from("xiaohuang")
      };
    s.print_name(); 
  }