# Function rand::random [−][src]

`pub fn random<T>() -> T where`

Standard: Distribution<T>,

This is supported on

**crate features**only.`std`

and `std_rng`

## 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();
}
```