running simple demos

demo.rs

// use anyhow::Error; 

trait NonDis {
    fn foo() where Self: Sized {} 
    fn returns (&self ) -> Self where Self: Sized; 
    fn param(&self, other: Self) where Self: Sized {}
    fn typed<T> ( &self, x : T) where Self: Sized {}
}

struct S; 

impl NonDis for S {
    fn returns(&self) -> Self where Self : Sized { S } 
}
// fn say_hello(out: &mut dyn Write) -> std::io::Result<()> {
//     out.write_all(b"hello world\n" ) ; 
//     out.flush()
// }

pub trait Summary {
    fn summarize(&self) -> String; 
}

pub struct NewsArticle {
    pub headline: String,
    pub location: String,
    pub author: String,
    pub content: String,
}

impl Summary for NewsArticle {
    fn summarize(&self) -> String {
        format!("{}, by {}, ({})", self.headline, self.author, self.location) 
    }
}


pub struct Tweet {
    pub username: String,
    pub content: String,
    pub reply: bool,
    pub retweet: bool,
}

impl Summary for Tweet {
    fn summarize(&self) -> String {
        format!("{}: {}", self.username, self.content)
    }
}

pub fn notify(item : &impl Summary ) {
    println!("breaking {}" , item.summarize())
}
fn main() {

let tweet = Tweet {
        username: String::from("horse_ebooks"),
        content: String::from(
            "of course, as you probably already know, people",
        ),
        reply: false,
        retweet: false,
    };
    println!("1 new tw : {}" , tweet.summarize() ) ; 
    notify(&tweet)
}