Traits（特質）

// 特質
pub trait Summary {
    fn summarize(&self) -> String;
}
pub struct NewsArticle {
    pub headline: String,
    pub location: String,
    pub author: String,
    pub content: String,
}
// 實現特質
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,
}
// 實現特質
impl Summary for Tweet {
    fn summarize(&self) -> String {
        format!("{}: {}", self.username, self.content)
    }
}
// 使用特質
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 tweet: {}", tweet.summarize());
// 缺省實現
pub trait Summary {
    fn summarize(&self) -> String {
        String::from("(Read more...)")
    }
}
// 使用特質的缺省實現
let article = NewsArticle {
    headline: String::from("Penguins win the Stanley Cup Championship!"),
    location: String::from("Pittsburgh, PA, USA"),
    author: String::from("Iceburgh"),
    content: String::from("The Pittsburgh Penguins once again are the best
    hockey team in the NHL."),
};
println!("New article available! {}", article.summarize());
// 有缺省實現的方法可以調用沒有缺省實現的方法
pub trait Summary {
    fn summarize_author(&self) -> String;
    fn summarize(&self) -> String {
        format!("(Read more from {}...)", self.summarize_author())
    }
}
impl Summary for Tweet {
    fn summarize_author(&self) -> String {
        format!("@{}", self.username)
    }
}
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 tweet: {}", tweet.summarize());
// 作為參數類型的特質
pub fn notify(item: impl Summary) {
    println!("Breaking news! {}", item.summarize());
}
pub fn notify<T: Summary>(item: T) {
    println!("Breaking news! {}", item.summarize());
}
// 兩個特質類型的參數
pub fn notify(item1: impl Summary, item2: impl Summary) {
pub fn notify<T: Summary>(item1: T, item2: T) {
// 多個特質
fn some_function<T: Display + Clone, U: Clone + Debug>(t: T, u: U) -> i32 
// where 子句
fn some_function<T, U>(t: T, u: U) -> i32
    where T: Display + Clone,
          U: Clone + Debug
{
// 返回特質
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,
    }
}
// 根據特質選擇性地實現方法
use std::fmt::Display;
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) {
        if self.x >= self.y {
            println!("The largest member is x = {}", self.x);
        } else {
            println!("The largest member is y = {}", self.y);
        }
    }
}
 

泛型

// 泛型函數
fn largest<T: PartialOrd + Copy>(list: &[T]) -> T {
    let mut largest = list[0];
    for &item in list.iter() {
        if item > largest {
            largest = item;
        }
    }
    largest
}
let number_list = vec![34, 50, 25, 100, 65];
let result = largest(&number_list);
println!("The largest number is {}", result);
let char_list = vec!['y', 'm', 'a', 'q'];
let result = largest(&char_list);
println!("The largest char is {}", result);
// 泛型結構
struct Point<T> {
    x: T,
    y: T,
}
let integer = Point { x: 5, y: 10 };
let float = Point { x: 1.0, y: 4.0 };
// 帶兩個類型參數的泛型結構
struct Point<T, U> {
    x: T,
    y: U,
}
let both_integer = Point { x: 5, y: 10 };
let both_float = Point { x: 1.0, y: 4.0 };
let integer_and_float = Point { x: 5, y: 4.0 };
// 標準庫中的泛型枚舉
enum Option<T> {
    Some(T),
    None,
}
enum Result<T, E> {
    Ok(T),
    Err(E),
}
// 泛型方法
struct Point<T> {
    x: T,
    y: T,
}
impl<T> Point<T> {
    fn x(&self) -> &T {
        &self.x
    }
}
let p = Point { x: 5, y: 10 };
println!("p.x = {}", p.x());
// 針對具體類型實現泛型結構的方法（==C++的全特化）
impl Point<f32> {
    fn distance_from_origin(&self) -> f32 {
        (self.x.powi(2) + self.y.powi(2)).sqrt()
    }
}
// 帶類型參數的泛型方法
struct Point<T, U> {
    x: T,
    y: U,
}
impl<T, U> Point<T, U> {
    fn mixup<V, W>(self, other: Point<V, W>) -> Point<T, W> {
        Point {
            x: self.x,
            y: other.y,
        }
    }
}
let p1 = Point { x: 5, y: 10.4 };
let p2 = Point { x: "Hello", y: 'c'};
let p3 = p1.mixup(p2);
println!("p3.x = {}, p3.y = {}", p3.x, p3.y);
 

Rust語言學習筆記（6）