Rust 程式設計影片教程(進階)——001 泛型

linghuyichong發表於2020-01-07

頭條地址:https://www.ixigua.com/i677586170644791348...
B站地址:https://www.bilibili.com/video/av81202308/

1、泛型是具體型別或者其它屬性的抽象替代,用於減少程式碼重複。

2、在函式定義中使用泛型。
例子:
++++++++不使用泛型+++++++++++

//for i32
fn largest_i32(list: &[i32]) -> i32 {
    let mut leargest = list[0];
    for &item in list.iter() {
        if item > largest {
            largest = item;
        }
    }
    largest
}

//for char
fn largest_char(list: &[char]) -> char {
    let mut leargest = list[0];
    for &item in list.iter() {
        if item > largest {
            largest = item;
        }
    }
    largest
}

fn main(){
    let number_list = vec![1, 2, 22, 3, 42];
    let r1 = largest_i32(&number_list);
    println!("r1 = {}", r1);
    let char_list = vec!['a', 'y', 'c', 'd'];
    let r2 = largest_char(&char_list);
    println!("r2 = {}", r2);
}
//+++++++++使用泛型:會報錯的函式++++++++++++
fn largest<T:PartialOrd + Copy>(list: &[T]) -> T { //注意,要實現比較和複製的trait才行,否則報錯
    let mut largest = list[0];
    for &item in list.iter() {
        if item > largest {
            largest = item;
        }
    }
    largest
}

fn main(){
    let number_list = vec![1, 2, 22, 3, 42];
    let r1 = largest_i32(&number_list);
    println!("r1 = {}", r1);
    let char_list = vec!['a', 'y', 'c', 'd'];
    let r2 = largest_char(&char_list);
    println!("r2 = {}", r2);
}

3、在結構體中使用泛型。
例子1:

#[derive(Debug)]
struct Point<T> {
    x: T,
    y: T,
}

fn main() {
    let integer = Point {x: 1, y: 2};
    println!("{:#?}", integer);
    let float = Point {x: 0.99, y: 1.99};
    println!("{:#?}", float);
}

例子2:

#[derive(Debug)]
struct Point<T, U> {
    x: T,
    y: U,
}

fn main() {
    let a = Point {x: 1, y: 2.0};
    println!("{:#?}", a);
    let b = Point {x: 1, y: 1.99};
    println!("{:#?}", b);
}

4、列舉中的泛型

//複習
enum Option<T> {
    Some(T),
    None,
}

enum Result<T, E> {
    Ok(T),
    Err(e),
}

5、方法中的泛型

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

impl<T> Point<T> {
    fn get_x(&self) -> &T {
        &self.x
    }
    fn get_y(&self) -> &T {
        &self.y
    }
}
fn main() {
    let p = Point {x: 1, y: 2};
    println!("p.x = {}", p.get_x());
    println!("p.y = {}", p.get_y());
}

例子2:方法和結構體中使用不同的型別

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,
        }
    }
}
fn main() {
    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);
}

6、使用泛型並不會造成程式效能上的損失。rust透過在編譯時進行泛型程式碼的單態化來保證效率。單態化時透過填充編譯時使用的具體型別,將通用程式碼轉換為特定程式碼的過程。

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