保存type到struct(使用PhantomData)

[wuyuedefeng]

use std::marker::PhantomData;
struct Dog<T: Hello> {
    _mark: PhantomData<T>
}

impl<T: Hello> Dog<T> {
    fn new() -> Dog<T> {
        T::hello();
        Dog {
            _mark: PhantomData
        }
    }
    fn hello(&self) {
        T::hello();
    }
}

trait Hello: Sized {
    fn hello() {
        println!("hello");
    }
    fn query() -> Dog<Self> {
        Dog::new()
    }
}

fn main() {
    struct Cat {}
    impl Hello for Cat {}
    
    let dog = Cat::query();
    dog.hello();
    
}