use std::fmt::Display;

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

    fn summarize(&self) -> String {
        format!("(Read more...) {}", self.summarize_author())
    }
}

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

impl Summary for NewsAritcle {
    fn summarize_author(&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_author(&self) -> String {
        format!("{}, {}", self.username, self.content)
    }
}

pub fn notify(item: impl Summary + Display) {
    println!("Breaking news! {}", item.summarize());
}

pub fn notify2<T: Summary + Display>(item: T) {
    println!("Breaking news! {}", item.summarize());
}

pub fn notify3<T>(item: T)
where
    T: Summary + Display,
{
    println!("Breaking news! {}", item.summarize());
}

pub fn notify5<T>() -> impl Summary
where
    T: Summary,
{
    Tweet {
        username: String::from("今日说法"),
        content: String::from("今日说法"),
        reply: true,
        retweet: false,
    }
}

struct Pair<T> {
    x: T,
    y: T,
}

impl<T> Pair<T> {
    fn new(x: T, y: T) -> Self {
        Self { x, y }
    }
}

impl<T: Display + PartialOrd> Pair<T> {
    fn cmp_display(&self) {
        println!("{}, {}", self.x, self.y);
    }
}