Function rand::random

source · [−]

pub fn random<T>() -> Twhere
    Standard: Distribution<T>,

Expand description

Generates a random value using the thread-local random number generator.

+

This is simply a shortcut for thread_rng().gen(). See thread_rng for +documentation of the entropy source and Standard for documentation of +distributions and type-specific generation.

+

Provided implementations

+

The following types have provided implementations that +generate values with the following ranges and distributions:

+

Integers (i32, u32, isize, usize, etc.): Uniformly distributed +over all values of the type.
char: Uniformly distributed over all Unicode scalar values, i.e. all +code points in the range 0...0x10_FFFF, except for the range +0xD800...0xDFFF (the surrogate code points). This includes +unassigned/reserved code points.
bool: Generates false or true, each with probability 0.5.
Floating point types (f32 and f64): Uniformly distributed in the +half-open range [0, 1). See notes below.
Wrapping integers (Wrapping<T>), besides the type identical to their +normal integer variants.

+

Also supported is the generation of the following +compound types where all component types are supported:

+

Tuples (up to 12 elements): each element is generated sequentially.
Arrays (up to 32 elements): each element is generated sequentially; +see also Rng::fill which supports arbitrary array length for integer +types and tends to be faster for u32 and smaller types.
Option<T> first generates a bool, and if true generates and returns +Some(value) where value: T, otherwise returning None.

+

Examples

+

let x = rand::random::<u8>();
+println!("{}", x);
+
+let y = rand::random::<f64>();
+println!("{}", y);
+
+if rand::random() { // generates a boolean
+    println!("Better lucky than good!");
+}

+

If you’re calling random() in a loop, caching the generator as in the +following example can increase performance.

+ +

use rand::Rng;
+
+let mut v = vec![1, 2, 3];
+
+for x in v.iter_mut() {
+    *x = rand::random()
+}
+
+// can be made faster by caching thread_rng
+
+let mut rng = rand::thread_rng();
+
+for x in v.iter_mut() {
+    *x = rng.gen();
+}

+