在 Rust 中自定义的数据类型主要是通过下面两个关键字:
-
struct: 定义结构体 -
enum: 定义枚举类型
常量是用const和static这两个关键字来声明.
1. 结构体
用struct关键字能够定义三种不同的结构体:
- 最基本的元组结构体,又叫元组(Tupels)
- 经典的类C结构体
- 单元结构体(泛结构体?)没有成员
示例
// A unit struct
// 单元结构体(泛结构体?)
struct Nil;
// A tuple struct
// 元组结构体
struct Pair(i32, f64);
// A struct with two fields
// 拥有两个成员的结构体
struct Point {
x: f64,
y: f64,
}
// Structs can be reused as fields of another struct
// 结构体能够作为其它结构体的成员
#[allow(dead_code)]
struct Rectangle {
p1: Point,
p2: Point,
}
fn main() {
// Instantiate a `Point`
// 实例化一个点
let point: Point = Point { x: 0.3, y: 0.4 };
// Access the fields of the point
// 访问改点的成员
println!("point coordinates: ({}, {})", point.x, point.y);
// Destructure the point using a `let` binding
// 用 let 分解,同时得到各成员值
let Point { x: my_x, y: my_y } = point;
let _rectangle = Rectangle {
// struct instantiation is an expression too
// 结构体的实例化是表达式,即有返回值
p1: Point { x: my_y, y: my_x },
p2: point,
};
// Instantiate a unit struct
// 实例化一个单元结构体
let _nil = Nil;
// Instantiate a tuple struct
// 实例化一个元组结构体
let pair = Pair(1, 0.1);
// Destructure a tuple struct
// 结构一个元组结构体
let Pair(integer, decimal) = pair;
println!("pair contains {:?} and {:?}", integer, decimal);
}
结果
point coordinates: (0.3, 0.4)
pair contains 1 and 0.1
2.枚举
enum关键字能够创建包含不同数据类型的类型.对struct有效的类型同样对enum有效.
示例
// An attribute to hide warnings for unused code.
// 对未使用的代码忽略警告
#![allow(dead_code)]
// Create an `enum` to classify someone. Note how both names
// and type information together specify the variant:
// 用` enum `创建一个"人"的类, 注意,名字和类型信息都是指特定的数据类型:
// `Skinny != Fat` and `Height(i32) != Weight(i32)`. Each
// is different and independent.
// `Skinny != Fat` and `Height(i32) != Weight(i32)`. 他们是不同的,独立的.
enum Person {
// An `enum` may either be `unit-like`,
// 一个枚举可以是 单元
Skinny,
Fat,
// like tuple structs,
// 元组
Height(i32),
Weight(i32),
// or like structures.
// 结构体
Info { name: String, height: i32 }
}
// A function which takes a `Person` enum as an argument and
// returns nothing.
// 一个需要传入 `Person`枚举作为参数,无返回值的函数.
fn inspect(p: Person) {
// Usage of an `enum` must cover all cases (irrefutable)
// so a `match` is used to branch over it.
// 枚举的使用必须覆盖所有条目,所以` match `里面有它所有的分支.
match p {
Person::Skinny => println!("Is skinny!"),
Person::Fat => println!("Is fat!"),
// Destructure `i` from inside the `enum`.
// 从枚举中分解出 ` i `
Person::Height(i) => println!("Has a height of {}.", i),
Person::Weight(i) => println!("Has a weight of {}.", i),
// Destructure `Info` into `name` and `height`.
// 分解出` Info ` 到 `name` and `height`.
Person::Info { name, height } => {
println!("{} is {} tall!", name, height);
},
}
}
fn main() {
let person = Person::Height(18);
let danny = Person::Weight(10);
// `to_owned()` creates an owned `String` from a string slice.
// `to_owned()`创建字符串切片的`String`类型.
let dave = Person::Info { name: "Dave".to_owned(), height: 72 };
let john = Person::Fat;
let larry = Person::Skinny;
inspect(person);
inspect(danny);
inspect(dave);
inspect(john);
inspect(larry);
}
结果
Has a height of 18.
Has a weight of 10.
Dave is 72 tall!
Is fat!
Is skinny!
2.1 use
用use关键字来代替获取.
// An attribute to hide warnings for unused code.
// 对未使用的代码忽略警告
#![allow(dead_code)]
enum Status {
Rich,
Poor,
}
enum Work {
Civilian,
Soldier,
}
fn main() {
// Explicitly `use` each name so they are available without
// manual scoping.
// ` use `带上每一个名字
use Status::{Poor, Rich};
// Automatically `use` each name inside `Work`.
// 自动` use `所有名字
use Work::*;
// Equivalent to `Status::Poor`.
// 等价于`Status::Poor`
let status = Poor;
// Equivalent to `Work::Civilian`.
// 等价于`Work::Civilian`
let work = Civilian;
match status {
// Note the lack of scoping because of the explicit `use` above.
// 注意不需要带上域(`Status`),因为明确地使用了`use`
Rich => println!("The rich have lots of money!"),
Poor => println!("The poor have no money..."),
}
match work {
// Note again the lack of scoping.
// 同样不用带上域(`Work`)
Civilian => println!("Civilians work!"),
Soldier => println!("Soldiers fight!"),
}
}
结果
The poor have no money...
Civilians work!
2.2. 类C枚举
enum 同样可以作为C中的枚举类型使用.
// An attribute to hide warnings for unused code.
// 对未使用的代码忽略警告
#![allow(dead_code)]
// enum with implicit discriminator (starts at 0)
//
enum Number {
Zero,
One,
Two,
}
// enum with explicit discriminator
enum Color {
Red = 0xff0000,
Green = 0x00ff00,
Blue = 0x0000ff,
}
fn main() {
// `enums` can be cast as integers.
println!("zero is {}", Number::Zero as i32);
println!("one is {}", Number::One as i32);
println!("roses are #{:06x}", Color::Red as i32);
println!("violets are #{:06x}", Color::Blue as i32);
}
结果
zero is 0
one is 1
roses are #ff0000
violets are #0000ff
2.3 测试用例:链表
枚举比较常见用来创建链表.
示例
use List::*;
enum List {
// Cons: Tuple struct that wraps an element and a pointer to the next node
Cons(u32, Box<List>),
// Nil: A node that signifies the end of the linked list
Nil,
}
// Methods can be attached to an enum
impl List {
// Create an empty list
fn new() -> List {
// `Nil` has type `List`
Nil
}
// Consume a list, and return the same list with a new element at its front
fn prepend(self, elem: u32) -> List {
// `Cons` also has type List
Cons(elem, Box::new(self))
}
// Return the length of the list
fn len(&self) -> u32 {
// `self` has to be matched, because the behavior of this method
// depends on the variant of `self`
// `self` has type `&List`, and `*self` has type `List`, matching on a
// concrete type `T` is preferred over a match on a reference `&T`
match *self {
// Can't take ownership of the tail, because `self` is borrowed;
// instead take a reference to the tail
Cons(_, ref tail) => 1 + tail.len(),
// Base Case: An empty list has zero length
Nil => 0
}
}
// Return representation of the list as a (heap allocated) string
fn stringify(&self) -> String {
match *self {
Cons(head, ref tail) => {
// `format!` is similar to `print!`, but returns a heap
// allocated string instead of printing to the console
format!("{}, {}", head, tail.stringify())
},
Nil => {
format!("Nil")
},
}
}
}
fn main() {
// Create an empty linked list
let mut list = List::new();
// Append some elements
list = list.prepend(1);
list = list.prepend(2);
list = list.prepend(3);
// Show the final state of the list
println!("linked list has length: {}", list.len());
println!("{}", list.stringify());
}
结果
linked list has length: 3
3, 2, 1, Nil