看了Bevy的示例：Rust还可以这样写

pub  fn type_name_of_val<T: ?Sized>(_val: &T) -> &'static str {
    type_name::<T>()
}
fn hello_world() {
    println!("hello world!");
}

fn  test2(){
    println!("test2 method");
}
trait  AddMethod:std::ops::FnMut(){
    fn  exec(&mut self){
        println!("start {} !",type_name_of_val(self));
        self();
        println!("end {} !",type_name_of_val(self));
    }
}
impl<T> AddMethod for T where T:FnMut(){}

fn main() {
   hello_world.exec(); // trait extension method  
   test2.exec();
}

结果

start test001::hello_world !
hello world!
end test001::hello_world !
start test001::test2 !    
test2 method
end test001::test2 !