mirror of https://github.com/sunface/rust-course
sunface
3 years ago
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# 场景化用例
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https://rust-lang-nursery.github.io/rust-cookbook/
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# 生成随机值
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## 生成随机数
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使用 [rand::thread_rng](https://docs.rs/rand/*/rand/fn.thread_rng.html) 可以获取一个随机数生成器 [rand::Rng](https://docs.rs/rand/0.8.5/rand/trait.Rng.html) ，该生成器需要在每个线程都初始化一个。
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整数的随机分布范围等于类型的取值范围，但是浮点数只分布在 `[0, 1)` 区间内。
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```rust,editable
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use rand::Rng;
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fn main() {
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let mut rng = rand::thread_rng();
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let n1: u8 = rng.gen();
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let n2: u16 = rng.gen();
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println!("Random u8: {}", n1);
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println!("Random u16: {}", n2);
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println!("Random u32: {}", rng.gen::<u32>());
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println!("Random i32: {}", rng.gen::<i32>());
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println!("Random float: {}", rng.gen::<f64>());
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}
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```
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## 指定范围生成随机数
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使用 [Rng::gen_range](https://rust-lang-nursery.github.io/rust-cookbook/algorithms/randomness.html) 生成 [0, 10) 区间内的随机数( 右开区间，不包括 `10` )。
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```rust,editable
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use rand::Rng;
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fn main() {
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let mut rng = rand::thread_rng();
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println!("Integer: {}", rng.gen_range(0..10));
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println!("Float: {}", rng.gen_range(0.0..10.0));
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}
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```
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[Uniform](https://docs.rs/rand/*/rand/distributions/uniform/struct.Uniform.html) 可以用于生成<ruby>均匀分布<rt>uniform distribution</rt></ruby>的随机数。当需要在同一个范围内重复生成随机数时，该方法虽然和之前的方法效果一样，但会更快一些。
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```rust,editable
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use rand::distributions::{Distribution, Uniform};
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fn main() {
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let mut rng = rand::thread_rng();
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let die = Uniform::from(1..7);
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loop {
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let throw = die.sample(&mut rng);
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println!("Roll the die: {}", throw);
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if throw == 6 {
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break;
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}
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}
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}
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```
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## 使用指定分布来生成随机数
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默认情况下，`rand` 包使用均匀分布来生成随机数，而 [rand_distr](https://docs.rs/rand_distr/*/rand_distr/index.html) 包提供了其它类型的分布方式。
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首先，你需要获取想要使用的分布的实例，然后在 [rand::Rng](https://docs.rs/rand/*/rand/trait.Rng.html) 的帮助下使用 [Distribution::sample](https://docs.rs/rand/*/rand/distributions/trait.Distribution.html#tymethod.sample) 对该实例进行取样。
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如果想要查询可用的分布列表，可以访问[这里](https://docs.rs/rand_distr/*/rand_distr/index.html)，下面的示例中我们将使用 [Normal](https://docs.rs/rand_distr/0.4.3/rand_distr/struct.Normal.html) 分布:
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```rust,editable
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use rand_distr::{Distribution, Normal, NormalError};
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use rand::thread_rng;
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fn main() -> Result<(), NormalError> {
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let mut rng = thread_rng();
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let normal = Normal::new(2.0, 3.0)?;
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let v = normal.sample(&mut rng);
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println!("{} is from a N(2, 9) distribution", v);
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Ok(())
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}
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```
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## 在自定义类型中生成随机值
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使用 [Distribution](https://docs.rs/rand/*/rand/distributions/trait.Distribution.html) 特征包裹我们的自定义类型，并为 [Standard](https://docs.rs/rand/*/rand/distributions/struct.Standard.html) 实现该特征，可以为自定义类型的指定字段生成随机数。
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```rust,editable
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use rand::Rng;
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use rand::distributions::{Distribution, Standard};
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#[derive(Debug)]
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struct Point {
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x: i32,
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y: i32,
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}
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impl Distribution<Point> for Standard {
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fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> Point {
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let (rand_x, rand_y) = rng.gen();
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Point {
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x: rand_x,
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y: rand_y,
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}
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}
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}
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fn main() {
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let mut rng = rand::thread_rng();
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// 生成一个随机的 Point
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let rand_point: Point = rng.gen();
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println!("Random Point: {:?}", rand_point);
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// 通过类型暗示( hint )生成一个随机的元组
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let rand_tuple = rng.gen::<(i32, bool, f64)>();
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println!("Random tuple: {:?}", rand_tuple);
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}
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```
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## 生成随机的字符串(A-Z, a-z, 0-9)
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通过 [Alphanumeric](https://docs.rs/rand/0.8.5/rand/distributions/struct.Alphanumeric.html) 采样来生成随机的 ASCII 字符串，包含从 `A-Z, a-z, 0-9` 的字符。
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```rust,editble
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use rand::{thread_rng, Rng};
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use rand::distributions::Alphanumeric;
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fn main() {
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let rand_string: String = thread_rng()
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.sample_iter(&Alphanumeric)
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.take(30)
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.map(char::from)
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.collect();
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println!("{}", rand_string);
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}
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```
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## 生成随机的字符串( 用户指定 ASCII 字符 )
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通过 [gen_string](https://docs.rs/rand/0.8.5/rand/trait.Rng.html#method.gen_range) 生成随机的 ASCII 字符串，包含用户指定的字符。
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```rust,editable
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fn main() {
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use rand::Rng;
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const CHARSET: &[u8] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZ\
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abcdefghijklmnopqrstuvwxyz\
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0123456789)(*&^%$#@!~";
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const PASSWORD_LEN: usize = 30;
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let mut rng = rand::thread_rng();
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let password: String = (0..PASSWORD_LEN)
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.map(|_| {
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let idx = rng.gen_range(0..CHARSET.len());
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CHARSET[idx] as char
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})
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.collect();
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println!("{:?}", password);
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}
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```
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@ -0,0 +1,3 @@
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## 课后习题
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[https://practice.rs](https://practice.rs)
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