use std::convert::From;

#[derive(Debug)]
struct Number {
value: i32,
}

impl From<i32> for Number {
fn from(item: i32) -> Self {
Number { value: item }
}
}

fn main() {
let int = 5;
// 试试删除类型说明
let num: Number = int.into();
println!("My number is {:?}", num);
}