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<main>
<h1 id="生成随机值"><a class="header" href="#生成随机值">生成随机值</a></h1>
<h3 id="生成随机数"><a class="header" href="#生成随机数">生成随机数</a></h3>
<p>使用 <a href="https://docs.rs/rand/*/rand/fn.thread_rng.html">rand::thread_rng</a> 可以获取一个随机数生成器 <a href="https://docs.rs/rand/0.8.5/rand/trait.Rng.html">rand::Rng</a> ，该生成器需要在每个线程都初始化一个。</p>
<p>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 <code>[0, 1)</code> 区间内。</p>
<pre><pre class="playground"><code class="language-rust editable edition2021">use rand::Rng;
fn main() {
let mut rng = rand::thread_rng();
let n1: u8 = rng.gen();
let n2: u16 = rng.gen();
println!(&quot;Random u8: {}&quot;, n1);
println!(&quot;Random u16: {}&quot;, n2);
println!(&quot;Random u32: {}&quot;, rng.gen::&lt;u32&gt;());
println!(&quot;Random i32: {}&quot;, rng.gen::&lt;i32&gt;());
println!(&quot;Random float: {}&quot;, rng.gen::&lt;f64&gt;());
}
</code></pre></pre>
<h3 id="指定范围生成随机数"><a class="header" href="#指定范围生成随机数">指定范围生成随机数</a></h3>
<p>使用 <a href="https://rust-lang-nursery.github.io/rust-cookbook/algorithms/randomness.html">Rng::gen_range</a> 生成 [0, 10) 区间内的随机数( 右开区间，不包括 <code>10</code> )。</p>
<pre><pre class="playground"><code class="language-rust editable edition2021">use rand::Rng;
fn main() {
let mut rng = rand::thread_rng();
println!(&quot;Integer: {}&quot;, rng.gen_range(0..10));
println!(&quot;Float: {}&quot;, rng.gen_range(0.0..10.0));
}
</code></pre></pre>
<p><a href="https://docs.rs/rand/*/rand/distributions/uniform/struct.Uniform.html">Uniform</a> 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。</p>
<pre><pre class="playground"><code class="language-rust editable edition2021">use rand::distributions::{Distribution, Uniform};
fn main() {
let mut rng = rand::thread_rng();
let die = Uniform::from(1..7);
loop {
let throw = die.sample(&amp;mut rng);
println!(&quot;Roll the die: {}&quot;, throw);
if throw == 6 {
break;
}
}
}
</code></pre></pre>
<h3 id="使用指定分布来生成随机数"><a class="header" href="#使用指定分布来生成随机数">使用指定分布来生成随机数</a></h3>
<p>默认情况下，<code>rand</code> 包使用均匀分布来生成随机数，而 <a href="https://docs.rs/rand_distr/*/rand_distr/index.html">rand_distr</a> 包提供了其它类型的分布方式。</p>
<p>首先，你需要获取想要使用的分布的实例，然后在 <a href="https://docs.rs/rand/*/rand/trait.Rng.html">rand::Rng</a> 的帮助下使用 <a href="https://docs.rs/rand/*/rand/distributions/trait.Distribution.html#tymethod.sample">Distribution::sample</a> 对该实例进行取样。</p>
<p>如果想要查询可用的分布列表，可以访问<a href="https://docs.rs/rand_distr/*/rand_distr/index.html">这里</a>，下面的示例中我们将使用 <a href="https://docs.rs/rand_distr/0.4.3/rand_distr/struct.Normal.html">Normal</a> 分布:</p>
<pre><pre class="playground"><code class="language-rust editable edition2021">use rand_distr::{Distribution, Normal, NormalError};
use rand::thread_rng;
fn main() -&gt; Result&lt;(), NormalError&gt; {
let mut rng = thread_rng();
let normal = Normal::new(2.0, 3.0)?;
let v = normal.sample(&amp;mut rng);
println!(&quot;{} is from a N(2, 9) distribution&quot;, v);
Ok(())
}
</code></pre></pre>
<h3 id="在自定义类型中生成随机值"><a class="header" href="#在自定义类型中生成随机值">在自定义类型中生成随机值</a></h3>
<p>使用 <a href="https://docs.rs/rand/*/rand/distributions/trait.Distribution.html">Distribution</a> 特征包裹我们的自定义类型，并为 <a href="https://docs.rs/rand/*/rand/distributions/struct.Standard.html">Standard</a> 实现该特征，可以为自定义类型的指定字段生成随机数。</p>
<pre><pre class="playground"><code class="language-rust editable edition2021">use rand::Rng;
use rand::distributions::{Distribution, Standard};
#[derive(Debug)]
struct Point {
x: i32,
y: i32,
}
impl Distribution&lt;Point&gt; for Standard {
fn sample&lt;R: Rng + ?Sized&gt;(&amp;self, rng: &amp;mut R) -&gt; Point {
let (rand_x, rand_y) = rng.gen();
Point {
x: rand_x,
y: rand_y,
}
}
}
fn main() {
let mut rng = rand::thread_rng();
// 生成一个随机的 Point
let rand_point: Point = rng.gen();
println!(&quot;Random Point: {:?}&quot;, rand_point);
// 通过类型暗示( hint )生成一个随机的元组
let rand_tuple = rng.gen::&lt;(i32, bool, f64)&gt;();
println!(&quot;Random tuple: {:?}&quot;, rand_tuple);
}
</code></pre></pre>
<h3 id="生成随机的字符串a-z-a-z-0-9"><a class="header" href="#生成随机的字符串a-z-a-z-0-9">生成随机的字符串(A-Z, a-z, 0-9)</a></h3>
<p>通过 <a href="https://docs.rs/rand/0.8.5/rand/distributions/struct.Alphanumeric.html">Alphanumeric</a> 采样来生成随机的 ASCII 字符串，包含从 <code>A-Z, a-z, 0-9</code> 的字符。</p>
<pre><pre class="playground"><code class="language-rust editble edition2021">use rand::{thread_rng, Rng};
use rand::distributions::Alphanumeric;
fn main() {
let rand_string: String = thread_rng()
.sample_iter(&amp;Alphanumeric)
.take(30)
.map(char::from)
.collect();
println!(&quot;{}&quot;, rand_string);
}
</code></pre></pre>
<h3 id="生成随机的字符串-用户指定-ascii-字符-"><a class="header" href="#生成随机的字符串-用户指定-ascii-字符-">生成随机的字符串( 用户指定 ASCII 字符 )</a></h3>
<p>通过 <a href="https://docs.rs/rand/0.8.5/rand/trait.Rng.html#method.gen_range">gen_string</a> 生成随机的 ASCII 字符串，包含用户指定的字符。</p>
<pre><pre class="playground"><code class="language-rust editable edition2021">fn main() {
use rand::Rng;
const CHARSET: &amp;[u8] = b&quot;ABCDEFGHIJKLMNOPQRSTUVWXYZ\
abcdefghijklmnopqrstuvwxyz\
0123456789)(*&amp;^%$#@!~&quot;;
const PASSWORD_LEN: usize = 30;
let mut rng = rand::thread_rng();
let password: String = (0..PASSWORD_LEN)
.map(|_| {
let idx = rng.gen_range(0..CHARSET.len());
CHARSET[idx] as char
})
.collect();
println!(&quot;{:?}&quot;, password);
}
</code></pre></pre>
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