Structs

Struct

struct User {
    active: bool,
    username: String,
    email: String,
    sign_in_count: u64,
}

fn build_user(email: String, username: String) -> User {
    User {
        email,
        username,
        active: true,
        sign_in_count: 1,
    }
}

let user1 = User {
    email: String::from("someone@example.com"),
    username: String::from("username123"),
    active: true,
    sign_in_count: 1,
};

let user2 = User {
    email: String::from("another@example.com"),
    ..user1
};

Tuple Struct

struct Color(i32, i32, i32);
struct Point(i32, i32, i32);
let black = Color(0, 0, 0);
let origin = Point(0, 0, 0);

newtype: Wrap type into tuple struct:

• Make code more readable.
• Implement 3rd traits for 3rd types.
• Hide internal details of types.

struct Meters(u32);

Unit-like Struct

struct AlwaysEqual;
let subject = AlwaysEqual;
impl SomeTrait for AlwaysEqual {}

Method

struct Circle {
    x: f64,
    y: f64,
    radius: f64,
}

impl Circle {
    fn new(x: f64, y: f64, radius: f64) -> Circle {
        Circle {
            x,
            y,
            radius,
        }
    }

    fn area(&self) -> f64 {
        std::f64::consts::PI * (self.radius * self.radius)
    }
}

enum Message {
    Quit,
    Move { x: i32, y: i32 },
    Write(String),
    ChangeColor(i32, i32, i32),
}

impl Message {
    fn call(&self) {}
}

fn main() {
    let m = Message::Write(String::from("hello"));
    m.call();
}

Self

• self: 所有权转移.
• &self: 不可变借用.
• &mut self: 可变借用.

pub struct Rectangle {
    width: u32,
    height: u32,
}

impl Rectangle {
    pub fn new(width: u32, height: u32) -> Self {
        Rectangle { width, height }
    }
    pub fn width(&self) -> u32 {
        return self.width;
    }
    pub fn height(&self) -> u32 {
        return self.height;
    }
}

fn main() {
    let rect = Rectangle::new(30, 50);
    println!("{}", rect.width());
    println!("{}", rect.height());
}

Generics

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

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

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

impl<T> Point<T> {
    fn x(&self) -> &T {
        &self.x
    }

    fn mixup<U>(self, other: Point<U>) {}
}

impl Point<f32> {
    fn distance_from_origin(&self) -> f32 {
        (self.x.powi(2) + self.y.powi(2)).sqrt()
    }
}

fn add<T: std::ops::Add<T, Output = T>>(a:T, b:T) -> T {
    a + b
}

fn largest<T: PartialOrd>(list: &[T]) -> T {}

• TurboFish:
  • generics_struct::<T>::method().
  • struct.generics_method::<T>().
• Use associated types in traits.

Traits

pub struct Post {
    pub username: String,
    pub content: String
}

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

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

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

fn main() {
    let post = Post{username: "username".to_string(),content: "content".to_string()};
    println!("1 new post: {}", post.summarize());
}

Orphan Rule

Rust can’t implement external traits on external types: can’t implement the Display trait on Vec<T> in some_package crate, because Display and Vec<T> are both defined out of some_package. This restriction is part of a property of programs called coherence, ensures that other people’s code can’t break your code and vice versa.

Trait Bound

fn notify(item: &impl Summary) {}
fn notify(item: &(impl Summary + Display)) {}
fn notify<T: Summary>(item: &T) {}
fn notify<T: Summary + Display>(item: &T) {}
fn notify<T, U>(t: &T, u: &U) -> i32
    where T: Display + Clone,
          U: Clone + Debug
{}

trait SomeTrait: BoundTrait {}

// 可以对任何实现了 Display 特征的类型调用 ToString 特征中方法.
impl<T: Display> ToString for T {}

Trait Derive

#[derive(Debug)]
#[derive(PartialEq)]
#[derive(Eq)]
#[derive(PartialOrd)]
#[derive(Ord)]
#[derive(Clone)]
#[derive(Copy)]
#[derive(Hash)]
#[derive(Default)]

trait Person {
    fn name(&self) -> String;
}

trait Student: Person {
    fn university(&self) -> String;
}

trait Programmer {
    fn fav_language(&self) -> String;
}

trait CompSciStudent: Programmer + Student {
    fn git_username(&self) -> String;
}

fn comp_sci_student_greeting(student: &dyn CompSciStudent) -> String {
    format!(
        "My name is {} and I attend {}. My language is {}. My Git username is {}",
        student.name(),
        student.university(),
        student.fav_language(),
        student.git_username()
    )
}

Trait Object

• Define trait object:
  • Box<dyn some_trait>.
  • &dyn some_trait.
• A trait can have trait object only when it is object safe:
  • all methods can't return Self.
  • all methods can't be generics.
• Trait object has 'static lifetime.
• Trait object stand for dynamic distributing (runtime), generics stand for static distributing (compile time).

trait Draw {
    fn draw(&self) -> String;
}

impl Draw for u8 {
    fn draw(&self) -> String {
        format!("u8: {}", *self)
    }
}

impl Draw for f64 {
    fn draw(&self) -> String {
        format!("f64: {}", *self)
    }
}

fn draw1(x: Box<dyn Draw>) {
    x.draw();
}

fn draw2(x: &dyn Draw) {
    x.draw();
}

fn main() {
    let x = 1.1f64;
    let y = 8u8;

    draw1(Box::new(x));
    draw1(Box::new(y));
    draw2(&x);
    draw2(&y);
}

Associated Types

Associated types make code become readable and concise:

trait Container<A,B> {
    fn contains(&self,a: A,b: B) -> bool;
}

fn difference<A,B,C>(container: &C) -> i32
  where
    C : Container<A,B> {}

trait Container{
    type A;
    type B;
    fn contains(&self, a: &Self::A, b: &Self::B) -> bool;
}

fn difference<C: Container>(container: &C) {}

For all generic trait, use associated types better than <T>.

Common Traits

• std::fmt::Display (better than std::string::ToString).
• std::fmt::Debug.
• std::ops::Add/Mul/Div/BitAnd/BitOr/Not/Neg: operators overload.
• std::ops::Fn/FnMut/FnOnce.
• std::ops::Deref.
• std::ops::Drop.
• std::clone::Clone.
• std::iter::Iterator.

std::prelude:

• std::marker::{Copy, Send, Sized, Sync, Unpin}.
• std::ops::{Drop, Fn, FnMut, FnOnce}.
• std::mem::drop.
• std::boxed::Box.
• std::borrow::ToOwned.
• std::clone::Clone.
• std::cmp::{PartialEq, PartialOrd, Eq, Ord}.
• std::convert::{AsRef, AsMut, Into, From}.
• std::default::Default.
• std::iter::{Iterator, Extend, IntoIterator, DoubleEndedIterator, ExactSizeIterator}.
• std::option::Option::{self, Some, None}.
• std::result::Result::{self, Ok, Err}.
• std::string::{String, ToString}.
• std::vec::Vec.
• std::convert::{TryFrom, TryInto}.
• std::iter::FromIterator.

use std::io::prelude::*;