t_wの輪郭

pub fn notify(item: &(impl Summary + Display)) {

pub fn notify<T: Summary + Display>(item: &T) {

pub fn notify<T>(item: &T) where T:Summary + Display {

→pub fn notify<T>(item: &T) where T:Summary + Display {

https://doc.rust-jp.rs/book-ja/ch10-02-traits.html#複数のトレイト境界を構文で指定する

fn returns_summarizable() -> impl Summary {
    Tweet {
        username: String::from("horse_ebooks"),
        content: String::from(
            "of course, as you probably already know, people",
        ),
        reply: false,
        retweet: false,
    }
}

https://doc.rust-jp.rs/book-ja/ch10-02-traits.html#トレイトを実装している型を返す

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

https://doc.rust-jp.rs/book-ja/ch10-02-traits.html#引数としてのトレイト

特質境界構文の糖衣構文となっている

trait Summary {
    fn summarize(&self) -> String {
        String::from("(Read more...)")
    }
}

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

impl Summary for NewsArticle {}

fn main() {
    let news_article = NewsArticle{
        headline: String::from("Headline"), 
        location: String::from("somewhere"), 
        author: String::from("somebody"), 
        content: String::from("something")
    };

    println!("{}", news_article.summarize());
}

https://doc.rust-jp.rs/book-ja/ch10-02-traits.html#デフォルト実装

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

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)
    }
}

fn main() {
    let news_article = NewsArticle{
        headline: String::from("Headline"), 
        location: String::from("somewhere"), 
        author: String::from("somebody"), 
        content: String::from("something")
    };

    println!("{}", news_article.summarize());
}

https://doc.rust-jp.rs/book-ja/ch10-02-traits.html#トレイトを型に実装する

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

https://doc.rust-jp.rs/book-ja/ch10-02-traits.html#トレイトを定義する

struct Body {
    weight: f64,
    height: f64,
}

impl Body {
    fn bmi_calc(&self) -> f64 {
        self.weight/(self.height*self.height)
    }
}

fn main() {
    let body = Body{weight: 60., height: 1.7};
    let bmi = body.bmi_calc();
    println!("bmi: {}", bmi);   //20.761245674740486
}