# Sugar ## Week 0C ---- ## Introduction + 語法糖 Syntactic Sugar + 簡化語法結構 + 增加程式碼的可讀性 + 但功能本身並沒有增加 --- # Structures ---- ## 宣告結構定義 ```rust= struct User { active: bool, user_name: String, email: String, sign_in_count: u64, } ``` ---- ## 宣告結構實體 ```rust= let mut user1 = User { active: true, user_name: String::from("Apple"), email: String::from("apple12345@example.com"), sign_in_count: 0, }; ``` ---- ## 把結構印出來 在宣告前面加上 `#[derive(Debug)]` <div style="font-size: 0.895em"> ```rust= #[derive(Debug)] struct User { user_name: String, email: String, } let u: User = ...; println!("{u:?}") // user: User { user_name: "apple", email: "apple@example.com" } ``` </div> ---- ## 修改欄位 ```rust= let mut user1 = User { ... }; user1.email = String::from("banana13579@gmail.com"); ``` ---- ## 初始化語法糖 ```rust= struct User { user_name: String, email: String, } fn init_user(user_name: String, email: String) -> User { return User { user_name, email }; } ``` ---- ## 無欄位名稱的結構 ```rust= struct Point(i32, i32); struct Color(u8, u8, u8); let p = Point(21, 35); let c = Color(12, 34, 56); println!("Coord({}, {})", p.0, p.1); println!("RGB({}, {}, {})", c.0, c.1, c.2); ``` ---- ## 蝦米都沒有的結構 ```rust= struct WTF; let wtf = WTF; ``` --- # Enumerations ---- ## 基本語法 ```rust= enum Fruits { Apple, Banana, Cherry, } let fruit = Fruits::Apple; match fruit { Fruits::Apple => println!("It's Apple!"), Fruits::Banana => println!("It's Banana!"), Fruits::Cherry => println!("It's Cherry!"), } ``` ---- ## Option + `Option<T>` 是個內建的 Enum ```rust let b: Option<u8> = Some(16); ``` + 在 `Option` 裡面就可以放 `None` 了 ```rust let a: Option<u8> = None; ``` ---- ## 使用 match 取值 + 在 match 取值裡面，會強制要求你考慮 None 的情況 ```rust= let a: Option<u8> = None; let b: Option<u8> = Some(16); let c = match a { Some(val) => val, None => 255, }; ``` ---- ## if let 語法糖 ```rust= let config_max = Some(3f32); match config_max { Some(max) => println!("最大值被設為 {max}"), _ => (), } ``` ```rust= let config_max = Some(3f32); if let Some(max) = config_max { println!("最大值被設為 {max}") } ``` --- # Other ---- ## 神秘數字 + `3u8` 表示一個 `u8` 整數，其值為 3 + 同理也有 `7i16`, `3.14f32`, `94.87f64` 等數值 ---- ## dbg! ```rust= struct Rectangle { width: u32, height: u32, } let scale = 2; let rect1 = Rectangle { width: dbg!(30 * scale), height: 50, }; ```