<h2>ch5. Using Structs to Structure Related Data</h2> - HackMD

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width: 34px !important; height: 21px !important; border: none !important; float: right; margin-top: -7px; margin-right: -10px; } .my-icon-css { width: 100%; height: 200px; background-position:center; background-repeat: no-repeat; background-image:url('https://mir-s3-cdn-cf.behance.net/project_modules/disp/fe36cc42774743.57ee5f329fae6.gif'); } </style>  # <h2>ch5. Using Structs to Structure Related Data</h2> <div class="my-icon-css"></div> @Kais(VagrantPi) ###### tags: `Rust`, `簡報`, `Rust 讀書會` ---  ## Defining and Instantiating Structs ----  ### Defining Structs ```go struct User { username: String, email: String, sign_in_count: u64, active: bool, } ``` ----  Structs 跟 tuples 很像，一樣可以包含多種 type，跟 tuples 不同的是每個 value 都有一個 key，所以可以清楚知道該值是啥 ----  ### Instantiating Structs - key: value pairs - 不須按造順序 ```go let user1 = User { email: String::from("someone@example.com"), username: String::from("someusername123"), active: true, sign_in_count: 1, }; ``` ----  #### 裡面有寫到一個不錯的比喻 > the struct definition is like a general template for the type, and instances fill in that template with particular data to create values of the type ----  #### 更改值 ```go let mut user1 = User { email: String::from("someone@example.com"), username: String::from("someusername123"), active: true, sign_in_count: 1, }; user1.email = String::from("anotheremail@example.com"); ``` ----  #### return Instance ```go fn build_user(email: String, username: String) -> User { User { email: email, username: username, // 因為輸入參數名稱跟 struct 變數名稱一樣，所以可以改寫成 // email, // username, active: true, sign_in_count: 1, } } ``` ----  ##### Creating Instances From Other Instances With Struct Update Syntax ``` 新的 Instance 有部分資料跟使用其他的 Instance 時，可以透過 struct update syntax(..) 的方法將其餘沒寫到的變數資料補上 ``` ```go let user2 = User { email: String::from("another@example.com"), username: String::from("anotherusername567"), active: user1.active, sign_in_count: user1.sign_in_count, }; // -------------------------------------------------- let user2 = User { email: String::from("another@example.com"), username: String::from("anotherusername567"), ..user1 }; ``` ----  #### tuple structs ``` struct 跟 tuple 的混合型別，取值時是使用 index 值 ``` ```go struct Color(i32, i32, i32); struct Point(i32, i32, i32); let mut black = Color(0, 0, 0); let origin = Point(1, 2, 3); println!("{}", origin.1); // 2 black.0 = 1 println!("{}", black.0); // 1 ``` ---  ## An Example Program Using Structs ----  v0.1 ```go fn main() { let width1 = 30; let height1 = 50; println!( "The area of the rectangle is {} square pixels.", area(width1, height1) ); // The area of the rectangle is 1500 square pixels. } fn area(width: u32, height: u32) -> u32 { width * height } ``` ----   v.02(使用 tuple 重構) ```go fn main() { let rect1 = (30, 50); println!( "The area of the rectangle is {} square pixels.", area(rect1) ); } fn area(dimensions: (u32, u32)) -> u32 { dimensions.0 * dimensions.1 } ``` ----  v.03(使用 struct 重構) ```go struct Rectangle { width: u32, height: u32, } fn main() { let rect1 = Rectangle { width: 30, height: 50 }; println!( "The area of the rectangle is {} square pixels.", area(&rect1) ); } fn area(rectangle: &Rectangle) -> u32 { rectangle.width * rectangle.height } ``` ----  #### Adding Useful Functionality with Derived Traits 如果是著想印出 struct ```go struct Rectangle { width: u32, height: u32, } fn main() { let rect1 = Rectangle { width: 30, height: 50 }; println!("rect1 is {}", rect1); // error[E0277]: the trait bound `Rectangle: std::fmt::Display` is not satisfied // `Rectangle` cannot be formatted with the default formatter; try using // `:?` instead if you are using a format string } ``` ----  println! 在印出東西時 {} 可以包含著格式化特徵(Formatting traits) 而 Display 為預設值 ```bash nothing ⇒ Display ? ⇒ Debug x? ⇒ Debug with lower-case hexadecimal integers X? ⇒ Debug with upper-case hexadecimal integers o ⇒ Octal x ⇒ LowerHex X ⇒ UpperHex p ⇒ Pointer b ⇒ Binary e ⇒ LowerExp E ⇒ UpperExp ``` ----  之所以 Display 能印出原始 type，是因為都們很"單純"，所以可以清楚的知道要印出什麼，但 struct 不同，包東包西，struct 的 `key` `value` 間還隔著 `:`，所以到底該印那些你並沒有說，而 `error` 也有建議可以使用 `:?` 來試試 ----  當你試了之後會發現 ```go // error[E0277]: the trait bound `Rectangle: std::fmt::Debug` is not satisfied // `Rectangle` cannot be formatted using `:?`; if it is defined in your // crate, add `#[derive(Debug)]` or manually implement it ``` ----  ![](https://dvblobcdnjp.azureedge.net//Content/Upload/Popular/Images/2017-06/e99e6b5e-ca6c-4c19-87b7-dfd63db6381a_m.jpg) ----  #### 讓我們再印一次 ```go #[derive(Debug)] struct Rectangle { width: u32, height: u32, } fn main() { let rect1 = Rectangle { width: 30, height: 50 }; println!("rect1 is {:?}", rect1); // rect1 is Rectangle { width: 30, height: 50 } } ``` ----  #### 如果 struct 很大很複雜這樣我們會改用 `{:#?}` ```go // rect1 is Rectangle { // width: 30, // height: 50 // } ``` ---  ## Method Syntax ----  #### Defining Methods ```go #[derive(Debug)] struct Rectangle { width: u32, height: u32, } impl Rectangle { fn area(&self) -> u32 { self.width * self.height } } fn main() { let rect1 = Rectangle { width: 30, height: 50 }; println!( "The area of the rectangle is {} square pixels.", rect1.area() ); } ```  ----  #### Methods with More Parameters ```go fn main() { let rect1 = Rectangle { width: 30, height: 50 }; let rect2 = Rectangle { width: 10, height: 40 }; let rect3 = Rectangle { width: 60, height: 45 }; println!("Can rect1 hold rect2? {}", rect1.can_hold(&rect2)); println!("Can rect1 hold rect3? {}", rect1.can_hold(&rect3)); // want // Can rect1 hold rect2? true // Can rect1 hold rect3? false } ``` ----  ```go impl Rectangle { fn area(&self) -> u32 { self.width * self.height } fn can_hold(&self, other: &Rectangle) -> bool { self.width > other.width && self.height > other.height } } ``` ----  #### Associated Functions <span>Associated Functions 通常用於建立一個或某種資料型態(因為會直接 return struct 的 instance)</span> ```go impl Rectangle { fn square(size: u32) -> Rectangle { Rectangle { width: size, height: size } } } let sq = Rectangle::square(3); ``` ----  #### Multiple impl Blocks ```go impl Rectangle { fn area(&self) -> u32 { self.width * self.height } } impl Rectangle { fn can_hold(&self, other: &Rectangle) -> bool { self.width > other.width && self.height > other.height } } ``` ---  ## Thanks for listening ~