# uuid4

Generates an RFC UUID version 4 from 16 fresh random bytes.

## Signatures

```ts
export declare const uuid4: Effect.Effect<Uuid4, never, RandomValues>;
```

## Why

Effectful generation exposes entropy as a service and explicitly sets version and variant bits; custom services must return a usable fresh buffer.

## Ownership and lifetime

The invocation mutates only its fresh byte buffer, acquires no persistent resource, and returns an immutable string.

## Examples

```ts
import { uuid4 } from "@typed/id/Uuid4"
import { RandomValues } from "@typed/id/RandomValues"
import { Effect } from "effect"
const id = Effect.provide(uuid4, RandomValues.Default)
```